Orvaskyte Keep

Orvaskyte Keep was a fortified outpost that marked northern border of Orva. It was destroyed by a magical disaster in and partially sank into the Vast Swamp.

Structure
Orvaskyte Keep consisted of a square walled fort with a large central keep, and a tall mage's tower in the north-east corner. It had a large underground complex beneath it.

The disaster entirely destroyed the central keep, leaving only a partially-melted shell. Most of the other buildings were ruined as the ground shifted, with the north-western corner of the Keep thrust upwards on a shelf of dirt and rock, while the eastern third of the Keep sank beneath the slimy waters of the Vast Swamp. A shrine to Chronos managed to survive almost intact along the northern wall.

The underground passages and rooms suffered terribly as well, partially collapsing as the earth rose and fell. Despite this, the sturdy stonework meant that it did not flood or entirely fall in on itself. The dungeon was incredibly humid and dank, filled with infectious diseases and vermin. The dungeons contained arcane laboratories as well as a prison for political enemies of the king.

Inhabitants
At the time of its destruction, the Keep was home to a garrison of approximately 500 soldiers, several archmages and high priests, and a collection of alchemists and other scholars.

By 1367 DR, Orvaskyte Keep was inhabited by a young black dragon, a cluster of gargoyles, and various other swamp-dwelling critters. The dungeons of the Keep contained a large amount of undead that had been trapped since it was destroyed, as well as a spirit naga in a magical ward set up by the original archmages as part of an experiment. A roaming cornugon also guarded the ruins, killing any intruders and gathering up black dragon eggs for some malefic purpose.

History
Around -702 DR, Orvaskyte Keep marked the northern bounds of the kingdom of Orva, amid the then-small and naturally formed Vast Swamp. The archmages of the Keep were tasked by their king to devise a means of expanding the realm's borders, on pain of death. Desperate to come up with a solution, they recklessly opened a portal to Minauros, one of the layers of Baator. This generated an explosion that destroyed the central structure of the Keep and killed most of the archmages, following by a great sucking wind that pulled the survivors and the responding high priests into the Hells.

Immediately after, a violent torrent of Minauros' slime washed out over the Keep and across the land, drowning much of Orva. This greatly expanded the Vast Swamp and transformed it into a noxious mire filled with diseases and monsters spawned from the Hells.

Although the gateway closed, the barrier between worlds remained thin and smaller portals to Minauros would erratically appear and disappear, allowing more of the Hells' influence to seep into Toril and depositing more horrors in the already-blighted landscape.

In 1367 DR, the Wolfmasters adventuring company attempted to explore and loot the ruins. The Wolfmasters had only just reached Orvaskyte Keep when they were set upon by the local cornugon, which slaughtered and dismembered them all. A few days later, an adventuring group from Cormyr sent to check on them arrived and explored the ruins, discovering artifacts and records originating from ancient Orva. Unfortunately, the Ruby Blades company arrived as well and managed to arouse the ire of a local adult black dragon, which pursued them and may have forced a large battle between between all the adventurers and the dragon.

Although the adventurers escape alive and laden with riches, the news that the miserable and noxious swamp was also infested with deadly fiends put an end to any plans of exploring the ruins further.