Arborea

The Olympian Glades of Arborea, also known as Olympus, was the Outer Plane in the Great Wheel cosmology model embodying the disorganized but well-intentioned motives of the chaotic good alignment. Its layers housed the elven and Greek pantheons, as well as the realms of the deities Lliira, Sune, and Tymora.

Although the gods of the realm of Olympus and Toril occasionally interacted, the people of Toril rarely concerned themselves with the affairs of the Olympians and vice versa. In the World Tree cosmology, the realms of Arvandor and Brightwater in the first layer were considered Celestial planes in their own rights. Arvandor, in particular, survived the Spellplague and became part of the World Axis cosmology.

Description
This plane had three layers with unique landscapes:

Arvandor
Sometimes referred to as Olympus; two realms, so vast and influential that their names became synonymous with the plane and the layer they occupied, coexisted with little conflict: Olympus, home of the Greek pantheon, and Arvandor, domain of the Seldarine. Even before the World Tree cosmology became popular, the influence of the Greek pantheon was primarily focused on other Prime Material Planes and had minor contact with the Forgotten Realms. Indeed, the two domains were separated by thousands of miles/kilometers of unclaimed wilderness and, due to the slight curvature of the landscape, were not visible to each other despite being located at the highest peaks of their respective lands. The layer also had a third realm known as Brightwater.

Dominating the Greek-controlled realms was Mount Olympus, a towering edifice that served as home to many of the Greek gods as well as a multiplanar conduit connecting Olympus directly to Hades, Gehenna, Tarterus, and Alternate Prime Material Planes without passing through the Astral Plane. The usual color pools existed for Astral travelers and the permanent portals to neighboring Outer planes Happy Hunting Grounds/Beastlands, Gladsheim, and Concordant Opposition took the form of large, spinning crimson disks. Divination was required to determine the destination of each portal and all pools and portals within thousands of miles/kilometers of the Greek or elvish demesnes were either guarded, surrounded by stone walls and iron gates, or both.

This layer was starkly mountainous with deep chasms, huge passes, and foothills the size of Prime plane mountains. Giant trees adorned the rugged terrain while the flatter parts were covered with untended vineyards, orchards and fields of wild wheat, eventually giving way to wilderness. Monsters and evil beasts took advantage of the lack of vigilance and roamed the wild places, providing a challenge to any who would go exploring.

Aquallor
Ossa to the Greeks and Aquallor to the elves, this layer was mostly filled with shallow seas no more than three feet (one meter) deep, with no islands or shores. The River Oceanus had its outlet here, delivering travelers from Elysium or the Happy Hunting Grounds/Beastlands safely in the middle of nowhere. The mighty sea was wracked with powerful storms. The shallow seabed was occasionally broken by cavernous trenches leading to undersea domains of various sea gods or by huge maelstroms that funneled water back to Thalasia in Elysium, thus completing the cycle. The barriers between layers of this plane were somewhat rare compared to other Outer planes. Being the middle layer, Aquallor had barriers that led to the watery realms of Poseidon and Deep Sashelas in Arvandor, as well as a few that lead to the third layer, Mithardir. Aquallor was also home to many sea elves and other aquatic creatures.

Mithardir
Also known as Pelion; Mithardir meant white dust in the Elven language, and the mysterious third layer was a land of blowing white sand, with snow in the colder regions. Both the Greeks and the elves had stories and legends about powerful beings who once lived here, creating artifacts and architecture that became all but buried in the dust after they presumably died or departed. Their fate, and that of any creatures left behind, remains unknown.

Inhabitants
Devas,, hollyphants, planetars, solars, foo creatures, and agathia formed the usual cohort of creatures ubiquitous to the Upper planes. But Arvandor was also the home of giant beasts and legendary monsters, such as giant bears, eagles, wolves, serpents, boars, lions, and wild cattle. Gorgons, cyclopes, giants, medusae, chimerae, harpies, sphinxes, and pegasi all made nests or lairs in the mountainous terrain or lived and lurked in the wilderness of the first layer.

Realms
Nearly all the known realms of this plane existed on the first layer.
 * Aerdrie Faenya, Seldarine Goddess of Air and Weather, wandered among the layers of Arvandor and Gladsheim accompanied by dozens of huge birds, taking her realm with her.
 * Corellon Larethian, chief deity of the Seldarine, once had a realm here.
 * Deep Sashelas, sea god of the Seldarine, inhabited the waters that bordered the other great elvish realms. Some sages put his realm named Elavandor in Aquallor.
 * Erevan Ilesere, Seldarine God of Mischief and Change, once made his home on this plane.
 * Finder Wyvernspur ascended to demigod status at the end of the Godswar and initially chose this plane for his realm, which he called Fermata.
 * Hanali Celanil, Seldarine Goddess of Romantic Love and Beauty, had a crystal palace here that surrounded an enchanted fountain which fed the magic pool Evergold (called Canathas by the Greeks).
 * Hlal, the draconic Jester, was know to lair somewhere on this plane, though the site was a secret.
 * Iallanis, giant goddess of love and beauty, had her realm of Florallium on the first layer.
 * Labelas Enoreth, elvish God of Longevity and rival to Erevan, once had a realm here.
 * Lliira, Goddess of Joy, Carefree Feeling, Contentment, Release, Hospitality, Happiness, Dance, and Patron of Festivals, once shared the welcoming realm of Brightwater on in this plane with several other goddesses.
 * Nephthys of the Mulhorandi pantheon had a large palace carved from rock which blended in with the desert far away from the demesnes of the Greek and the elves. Some sages put her realm called Amun-thys in Pelion/Mithardir.
 * Poseidon, god of waters, maintained his marine realm, Caletto, in Aquallor.
 * Rillifane Rallathil the Leaflord, whose realm was also his body, once put down his roots on this plane.
 * Sehanine Moonbow, the Daughter of the Night Skies, resided with Corellon in Arvandor.
 * Sharess, the Lustful Mistress, joined her fellow goddesses in the realm of Brightwater in Arvandor after the Time of Troubles.
 * Shevarash, the Black Archer, had no realm of his own, but often stayed within Arvandor.
 * Solonor Thelandira, God of Archery and Hunting, had a realm of thick forests and rapidly flowing streams named Pale Tree here.
 * Sune, human Goddess of Love, Beauty, Passion, and Charisma, once made her home, Brightwater, on this plane. She shares the waters of Evergold with Hanali Celanil.
 * Syranita, goddess of the aarakocra, had her realm named Whistledge in Olympus.
 * Tymora, human Goddess of Good Fortune, Luck, Victory, Skill, and Patron of Adventurers and Warriors, resided in the realm of Brightwater in Arvandor.