Undermountain

Undermountain was a multi-tiered dungeon, comprised of several inter-connected chambers and lairs located deep beneath the city of Waterdeep and its namesake mountain. Originally home to the dwarves of Clan Melairkyn, the Underhalls were home to a grand dwarfhold before they were taken over by the "Mad Mage" Halaster Blackcloak and his seven apprentices.

Architecture
As a general rule, Undermountain was a structure with high ceilings of at least 16 feet (4,8 meters) and smooth floors made of gray granite. Areas that were created by carving out a single rock were generally decorated in a way that made them look like other more standard areas. That said, exceptions existed.

A corridor in Undermountain was usually 10 feet (3 meters) wide and high. The stairs had no railings.

Magical Features
Undermountain had lots of magical peculiarities that were placed by Halaster. Undermountain's proprietor turned his place into one that made it impossible for magic that teleported people into or out of Undermountain to work. Various divination magic that could be used to gather information about what was ahead could not be used too. The limitation that was in place was divination magic that worked through objects, other spells like wizard eyes worked to some degree. Summoning spells also had difficulties to work. Their functionality was limited to snatching monsters that were already present in Undermountain. However, magic items that summoned creatures worked, at least as a general rule.

Destroying the wards that put these limitations was a task that was as good as impossible. On a pure theoretical level, it was possible. One needed a high understanding of magic to understand the many-layered magic, knowledge to determine how to dissolve it, the skill to make the dissolution actually happen, combat prowess to protect oneself from monsters that were certainly attracted to people working to dissolve the layered magic, a working speed that exceeded the speed at which the magic was restored, a lot of time measured at least in months, and the willingness to do this despite the work's doubtlessly thankless and likely fruitless nature.

Another effect of the many-layered magic of the Mad Mage was that most of the dungeon radiated magic including the floor, ceilings, and walls. This made spells like detect magic from time to time useless ones because either the radiated magic was so strong that it was impossible distinguish specific things like magic items or because the radiated magic worked as some kind of background noise that masked the radiated magic of other things.

Atmosphere
Undermountain had quite good ventilation due to a plethora of air sources and some magical support. While areas where the ventilation was bad existed, for example due to a sealed door or being connected to sewers, death from suffocation of gas explosion was not hazard that one needed to prepare for as high priority.

All in all, Undermountain's climate could be compared to a normal Waterdhavian cellar, cold and a bit dank. When an area was more humid than what was normal, it could mean that a water source was nearby, sometimes also fungal growth. When it was drier than normal, it usually meant that one was far from a water source.

Interestingly, deeper levels were a bit warmer than upper ones. This was attributed to volcanic activities, but this was more a theory than proven fact.

Entrances and exits
The halls of Undermountain were linked to the surface world in many ways, both physical and magical. Some worked only one-way.The dungeon had number of connections with Waterdeep's sewers and through this connection, it was indirectly connected to other dungeons. Halaster used his network of portals to bring in monsters from all across Faerûn to restock his dungeon. Some of the notable physical links are described below:


 * Blue Mermaid Passage: This connected a dry well in the cellar of the Blue Mermaid tavern to Skullport.
 * Castle Corkscrew: This passage corkscrewed down from the cellars of Castle Waterdeep to Skullport, bypassing the first two levels.
 * Falling Stair: This connected the dungeons of Castle Waterdeep and the Citadel of the Bloody Hand with Undermountain's first level.
 * Knight n'Shadow: Built over the ruins of the Sea Knight Tavern which collapsed in 1425 DR, the cellar of this tavern connected to Downshadow.
 * Long Dark Stair: This linked the oubliette or more a rubbish heap near the Blushing Nymph festhall with Undermountain's first level.
 * River Sargauth: This river ultimately led to the Sea of Swords.
 * The Yawning Portal Inn: Built atop the ruins of Halaster's Hold, The Yawning Portal Inn contained the only publicly known entrance into Undermountain: a large well that dropped down into Undermountain's Dungeon Level. There was also a second entrance in the form of a functional well.

Major Levels

 * The Dungeon Level:
 * The Dungeon Level was long used by the Lords of Waterdeep as a dumping ground for undesirables, hence its most common name. It was also known as the Temple Level, for the many temples of dark gods that were constructed here over the years, as well as the Tomb Level, for the many lords and kings that were interred here as well. As explorers of Undermountain often visited this level, its features were common tavern-talk of Waterdeep. Notable features of the Dungeon Level included the Bone Throne, the Cavern of Eyes, the Falling Stair, the Grim Statue, theHall of Sleeping Kings, the Hall of Three Lords, the House of Pain, the Lanceboard Room, the Sundered Throne, the Temple of Gulkulath, and the Temple of the All-Seeing One.


 * Arcane Chambers:
 * On this level, Halaster and his apprentices excavated the rough stone caverns and mining tunnels left by the dwarves to house their acquisitions and magical experiments. Notable features of the Arcane Chambers included the Doomgate, the Helmwatch, and Lord Hund Hillgauntlet's tomb.


 * The Sargauth Level:
 * Known for the River Sargauth, which winds through this massive level, Undermountain's third level consisted of two major sections. The southern portion of this level consisted of the remnants of the Sargauth Enclave, which was later split by a massive cave-in leading to Skullport and the Promenade of the Dark Maiden. The northern two-thirds of this level were constructed by Halaster and his apprentices, and served much the same role as Undermountain's second level. The most notable features of this level were the Lair of the Eye, the rubble-filled Pit of Ghaunadaur, a mile-deep shaft that led from the Prime Material Plane through an intermittently-existent planar breach into the Cauldron of Slime, along with the subterranean settlement of Stromkuhldur, among others.


 * Twisted Caverns:
 * Also known as the Farms, this level of Undermountain contained farms that no surface dweller would recognize. Halaster's mightiest magic brought the River of the Depths, also known as the River Sargauth, to this level, where it linked huge caverns in broad, sweeping curves, and was navigable by barges. Notable features included...


 * The Maze Level:
 * This level contained five major features of note - the drow outpost of Kyorlamshin, the lair of the Umber Hulks, the Maze of Madness, an old dwarf hold built by Clan Melairkyn and expanded by the duergar, and the winding channels of the River Graymurk.


 * The Seadeeps:
 * The Seadeeps had numerous connections to the Swordsea Depths, as the Underdark beneath the Sea of Swords is known.


 * The Caverns of Ooze:
 * The Caverns of Ooze were long home to all manner of slimy creatures serving That Which Lurks. Countless slimes, oozes, jellies, and other amorphous creatures frequented these natural caverns.


 * The Terminus Level:
 * Also known as the Deep Mines, this level was a mix of dwarf-built chambers, depleted mithral mines, and vast natural caverns. Many of the one-way portals used by Halaster to restock Undermountain with dangerous monsters opened into the sprawling caverns of Undermountain's eighth layer. Additionally, Halaster's failed or free experiments also wandered this level. The Terminus Level connected with the heart of Undermountain through the Shaft.


 * The Mad Wizard's Lair:
 * Said to hold the treasure of Halaster the Mad, this level was spoken about in Waterdhavian taverns late at night by those who dared to dream of plumbing the depths of Undermountain. Of course, Halaster himself spread many of these rumors, in hopes of inducing more adventurers to die foolish deaths in his trap-filled Underhalls.

Sub-Levels

 * The Waterdeep Sewers: Typical of many large cities, Waterdeep had its share of sewer passages beneath its streets. What was not typical of these sewer tunnels however, were the links to the famed Halls of Undermountain which ensured a constant supply of creatures to inhabit them and an even more constant supply of adventurers to combat them. Many adventurers also used the sewers as an access point, bypassing the more notable entrances to the dungeon complex below.


 * The Citadel of the Bloody Hand: Dug into the heart of Mount Waterdeep, the Citadel of the Bloody Hand has until recently been occupied by the Guard. After Halaster's Higharvestide, the Citadel of the Bloody Hand became the preserve for the living spells that escaped Halaster.


 * Wyllowood: Halaster created the Wyllowwood over two centuries before the Second Sundering for an elf druid named Wyllow, the beloved of his apprentice Yinark. Set in a cavernous region carved by a tributary of the River Sargauth, this thriving forest was nourished by sunlight filtered through a massive portal in the "sky" above. Notable features included a temple of the Destroyer and a long-abandoned lakeside village built by the dwarves of Clan Melairkyn.


 * Maddgoth's Castle: This small sub-level famed for the presence of the miniature, floating castle built by Halaster for his serial-killer apprentice Maddgoth. It was enveloped in a reduction field that reduced all creatures within it to one-twelfth their normal size.


 * The Lost Level: Entombed in solid rock, the Lost Level was almost entirely inaccessible.


 * The Slitherswamp: Located deep beneath the city of Waterdeep, the Slitherswamp was a largely unexplored sub-level between the Farms Level and the Maze Level.


 * Muiral's Graveyard: Muiral's Graveyard was a sub-level built by the drow soon after their initial invasion that included living quarters and a warrior academy. Muiral transformed these chambers into a trap-filled gauntlet haunted by giant spiders, undead, and driders. Although the monstrous mage abandoned this area, his deadly creations remained.


 * The Troglodyte Warrens: This region of caves was accessible only by a two-way random portal. It was home to two warring tribes of troglodytes - the Urggroth-Kyan clan and the Szygmog-Thurgin clan.


 * Trobriand's Graveyard: The dwarves originally mined this sub-level for mithral, leaving it, by chance or for mysterious reasons, in the crude image of a scorpion. Before Halaster's Higharvestide, the Realm of the Metal Masters was home to Trobriand's rejected constructs, built before he had perfected his scaldars. By Halaster's Higharvestide, Trobriand's cast-offs had organized themselves into a self-governing community for mutual defense, and they took advantage of the chaos to escape through a portal to their master's secret sanctum and claim it for themselves. In the wake of their departure, this level was largely abandoned, but it didn't remain that way for long. After being driven from Skullport by the Eye, Misker the Pirate Tyrant fled to this level and made it his own. Now a portal linked the beholder's lair to the Ilzimmer Villa, and House Ilzimmer began storing its ill-gotten gains there.


 * The Obstacle Course: The Obstacle Course was a sub-level composed of a long chain of trap-filled rooms. Carved from the earth by the will of Tyr, this sub-level was intended as a potentially lethal test for conceited, cocky braggarts who did not respect the dangers of adventuring.


 * Arcturiadoom: This level was long the private domain of Arcturis, one of Halaster's most ambitious apprentices. After her death during Halaster's Higharvestide, contingency magics whisked her corpse to her sanctuary, leaving the illusion of a body in their wake. Thanks to careful preparations, Arcturia was reborn as a vile form of undead. She now worked to restock the monsters guarding this level, which was known to a handful of daring explorers as Arcturiadoom.


 * The Crystal Labyrinth: The drow constructed this chamber as a training ground for their young in 148 DR. Halaster discovered it in 326 DR and made it his own, with transparent crystal walls, floors and ceilings, and a coral-floored cavern filled with seawater directly below. At the heart of the labyrinth lay Halaster's Aqitocrun, a treasure chamber in which he stored prized possessions.
 * Vanrakdoom: This sub-level was claimed by Lord Vanrak Moonstar for the followers of the Night Maiden in 1130 DR. A sprawling shadow-cloaked temple of Shar and an army of creatures from the Plane of Shadow that defended the abbey dominate Vanrakdoom.


 * The Runestone Level: Not much was known about this small sub-level located between The Caverns of Ooze and The Terminus Level. It remained largely unexplored though rumors stated it was linked to The Shaft by multiple small, twisting passages.


 * Shadowdusk Hold: This sub-level was among the deepest known sub-levels of Undermountain. It may or may not have been connected to Halaster's Lair which lay just seaward of this sub-level.

History
Aelinthaldaar, the capital city of Illefarn, was founded around –8500 DR and first started to dig crypts in the area. Various power groups lived in Undermountain, sometimes at the same time:

Melairkyn Clan
In -1288 DR, a shield dwarf called Melair explored and found mithril in the mountain that was later called Mount Waterdeep both for the first time. At that time however, it was called Mount Melairbode after Melair. Clan Melairkyn, a dwarven clan that eventually traced its ancestry back to Melair built in the same year the Underhalls inside the mountain. They then formed an arrangement with the elves of Illefarn, their mithril for the elves' magic, namely one that prevented the caverns to collapse no matter what. This clan of dwarves operated two mithril mines in the Seadeeps.

Around 34 DR, a combined force of drow and duergar forced the dwarves into deeper and unimportant sections of Underhalls. The mithril minies were taken over by the duergar, who left the place after the mines dried out. The drow continued to force the dwarves into ever lower and ever less important places until the dwarves died out in 211 DR. Underhalls was then named Kyorlamshin by the drow.

Halaster Blackcloak
In 168 DR, Halaster Blackcloak and his seven apprentices came to Kyorlamshin. To be more precise he built Halaster's Hold in the Deepwater Plateau. He used summoned creatures to dig cellars and the likes for himself. This was done often and in ever deeper areas for decades that at some point his creatures managed to break into the Underhalls. The mage started to explore the underground complex as well as staking claims for himself regarding the underground areas.

As mentioned above, the duergar were in the process of leaving once the mithral was running dry, when it came to the drow, they fell victim to surface elves and the remnants of these two parties fell victim to Halaster in 309 DR. Halaster modified captured drow into his servitors and entered a genocidal frenzy that led to the term "Halaster's Hunt" to be coined. This term meant "berserk raid" or "willful slaughter" and was still in use in the North of the 14 century DR. Halaster started to move into the underground complex and to modify it by building traps and turned the complex into a storage of his belongings, experiment results, and so on. His apprentices, who were already starting to carve out their own demenses by 307 DR, put serious effort in finding their master. Their mettle was tested by Halaster, two died, and the rest was employed by the Mad Mage to enhance the underground complex's security. Over the years, the upper levels became abandoned as a storage and research faculty, those functions were moved ever deeper into the complex. Halaster started to turn the upper levels into a buffer zone to kill intruders. Towards that end, he went to other planes and places, collected monsters, and set them out to protect these levels from intruders, this also had a touch as Halaster's playing ground as he started to use the dungeon to satisfy his hobbies.

In the year 658 DR, a portal was built in secret between the Hall of Naturalists in Cormanthyr and Undermountain. The Guild of Naturalists started to break into Halaster's property to abduct his monsters for themselves. Halaster started to abduct wizards from Cormanthyr as an act of retaliation. It was only in 680 DR that the Guild of Naturalists managed to understand that the abductions over the decade in between were done as a response to their actions. After seeing that an expedition team with the goal of bringing back their abductees did not come back, the Guild of Naturalists stopped poaching. However, they were incapable of shutting down the portal that connected the two places.

Waterdeep
At some point in history, Halaster came up with the idea to create a duplicate of himself, possibly a clone, infect it with leprosy, and let the eventual corpse be found by Waterdeep's police force. This led to the false information of Halaster's death be spread in Waterdeep. By 1371 DR, the notion of a powerful crazy wizard living in Undermountain was the stuff of rumors and not verified information. However, among Undermountain-travelers, it was common to at least think that he was still alive.

This false information about the Mad Mage's death's spreading's original intention by Halaster was to ensure that nobody bothered him while he was doing his research in his home. However, the idea that the powerful mage was dead led to many folks thinking that the major obstacle against plundering the wizard's place was gone. These people became burglars bent on taking whatever they could from Halaster's dungeon. Them getting killed by Halaster's traps and roaming creatures that he released was a major source of joy for the Mad Mage as was the false sense of security that his false death represented to people.

As Waterdeep grew as a city, the city came into contact with the dungeon. This included literal contact in the form of sewers that broke into Halaster's dungeon as they were dug. Lords of Waterdeep used the dungeon to get rid of criminals they considered particularly hard to handle in 1302 DR. This took the form of sending them from their prisons to uncharted parts of Undermountain. This last action at the hands of Waterdeep's rulers led to Undermountain getting a bad reputation overall and one as the deepest dungeon in the world, the latter was considered to be of dubious veracity.

Also in 1302 DR, Durnan the Wanderer and Mirt the Merciless went into Undermountain. Unlike many others, they did not just come out as a living men but also as rich ones. Durnan did two things: first, he built the Yawning Portal inn where Halaster's Hold's ruins stood. Second, he spread the information about Undermountain's size and wealth like others who successfully returned from the dungeon. This led many people for various reasons to go to Durnan's inn that held the shaft to enter the dungeon.

The Citadel of the Bloody Hand was the launching point of the Thieves' Guild of Waterdeep before they were driven out of the city.

Various criminal groups used portions of the ruins as their headquarters as do followers of evil gods. Halaster's death in 1375 DR and the earthquake that accompanied it altered terrain and also upset the balance of power among the various groups. It was around ten years later when the Spellplague occurred and once again drastic change came to Undermountain. Many of the numerous portals in the ruins were destroyed, cutting off entire levels. Other portals were warped and seemingly granted access to previously unknown levels. Also it was feared that pockets of Spellplague may still exist in Undermountain.

Undermountain and Halaster Blackcloak
Over a thousand years ago, the wizard Halaster Blackcloak whirled to the base of Mount Waterdeep, called there from a distant country by chance or providence. Some say he hailed from the Cradlelands, the nearly forgotten empire that spread humanity across Faerûn, Kara-Tur, and Zakhara, from what is now the Plains of Purple Dust, a wasteland created by conflict between the gods. Whatever his origins, Halaster brought with him the Seven, as his apprentices were known, and with their help and his power, Halaster summoned beings from other planes to build himself a wizard's tower. Halaster ringed his tower with a great wall set with lesser towers for each of his apprentices, and he created fields and farms to be worked by his apprentices and their servants.

For a time, it seemed a good life for the Seven, but as the days wore on, they saw less and less of their master. Halaster continued to use fell creatures from other planes for construction beneath his tower, and he kept his dealings with them and the nature of the tunnels from the Seven. At length, Halaster's tunneling broke into the Underhalls, a complex of tunnels built by dwarves around a mithral mine beneath Mount Waterdeep. The dwarves who built the dungeons, the Melairkyn clan, had long since been killed or dispersed, replaced by warring duergar and drow. Halaster began a crusade against both races, participating in wild hunts through the tunnels with allies called from the Outer Planes. The duergar stubbornly remained until the mithral was largely mined out, but then they left the drow to fight Halaster and his minions alone. Halaster captured or killed the remaining drow, entrapping their souls for dark magic or twisting their bodies and enslaving their minds. When the last of the drow were defeated, Halaster Blackcloak tunneled on, continuing his obsession with delving beneath the mountain.

After Halaster was absent for more than a year, some of his apprentices ventured into his tower in search of the great wizard. They found traps, monsters, and tantalizing hints about power beneath the earth. Individually they explored the dungeons, encountering ever more deadly traps and more powerful foes. For their efforts, they were rewarded with riches and magic. When the Seven were reduced to five, Halaster appeared to his students and explained that he had built the tunnels to guard his experiments and treasures. He enlisted their aid to make his dungeons even more secure.

What happened after that is unclear, but only one apprentice is known to have left Undermountain, and she fled the area, never to return. Halaster continued to live beneath the mountain, using it as a base from which he traveled to other planes and distant lands, entrapping strange creatures and bringing them back to live as prisoners or guardians in his home. In time, Halaster sought out magic to extend his life, and some say that it was these spells and items that finally drove Halaster beyond all reason. While before he had been obsessed and deranged, his quest for immortality seemed to drive him truly mad.

While Halaster quested on other planes and sequestered himself in his tunnels, his tower fell into ruin. When Halaster was yet active in the outside world, his home was considered cursed, so settlers in the area largely left the crumbling tower alone. In time, the city now known as Waterdeep came to huddle against the mountain and reach down to the harbor. As the city sprawled outward, it reached and encompassed the ruins of Halaster's home. Undermountain was known to these early settlers, and they often punished criminals by sending them into its depths. This continued for many years until an adventurer named Durnan delved into the depths beneath the tower and returned, laden with riches, to tell the tale. Durnan demolished the last remnants of Halaster's above-ground abode and built an inn over the well he had used to descend into the depths. He called his inn the Yawning Portal, and Durnan works there to this day, serving patrons and inviting the brave or the foolish to try their hands at the halls of Undermountain.

Timeline

 * -1288 DR: King Melair I discovers mithral ore underneath Mount Waterdeep and creates a home for his Melairkyn, beginning to carve out caverns and tunnels
 * -750 DR: Netherese wizards occupy the third level of Undermountain and seal it off against the Melairkyn. Some scholars call this the Sargauth Enclave
 * -677 DR: The drow begin to occupy more and more of the area held by the Melairkyn
 * 34 DR: In a large shift of territory following a massive drow invasion, the Melairkyn lose a lot of their territory
 * 168 DR: Halaster Blackcloak claims the Underhalls of the ousted Melairkyn for himself.
 * 171 DR: Halaster begins Halaster's Hunts which wipe out large numbers of the drow and duergar from Undermountain and continue until 308 DR. Many drow and duergar are forced out during this time.
 * 268 DR: The mithral is now completely depleted
 * 284 DR: The duergar leave Undermountain, having no reason to stay without the mithral resource
 * 309 DR: Halaster becomes ruler of the Underhalls
 * 493 DR: The drow leave Undermountain entirely
 * 1355 DR: Qilué Veladorn constructs the Promenade of the Dark Maiden - a temple of the good-aligned drow goddess Eilistraee - northeast of Skullport.
 * 1375 DR: Halaster Blackcloak dies.
 * 1385 DR: The Spellplague hits Undermountain, drastically altering the landscape of the dungeon.

Connections
Unterberg