Gehenna

The Bleak Eternity of Gehena is an outer plane located deep in the negative energy zone. It is the plane of extreme greed and, as a result, extreme suspicion. The plane is divided into four layers, each composed of a massive sloped volcano, and numerous floating earthmotes that crash into the four mountains unceremoniously. Gehenna is the home of the yugoloths and other fiends who embody the vices of suspicion and especially greed. With the sloped, harsh terrain and the hostile denizens, Gehenna is not a forgiving place for the casual traveler.
For more information on this plane, consult the 5th Edition Dungeon Master's Guide, page 63, or see the Forgotten Realms wiki: here.

The Deep Forge

Deep underneath one of the volcanoes rests the home of the dwarven deity Toldrun. Here, his dwarves and fiends dig deeper into the mountain, hoping to uncover valuable gems and ores or open a new stream of lava that can feed the many forges of the city. Toldrun himself lives in a lavish palace carved into a massive stalagmite, filled with some of the most valuable gems and metals in the universe - and the most well-paid guards to make sure they stay in place.

Host of Eyes and Ears

One of the other volcanic layers hosts a porous city carved into the volcanic rock, like a Pueblo dwelling of pure basalt and obsidian. The winds and hot air of the plane seem to all be swept into this city like a vacuum, as it absorbs everything around it. This is the home of the Olcrid Dur'dyn, the Mistress of Thieves and Spies. From this perch, she sends her minions out to other areas of the plane to steal from and spy on her enemies and unsuspecting travelers. The inside of this city is a labyrinth with twisting corridors that sometimes lead to dead ends and other times lead to vast treasuries of gems and gold.

The Crone's Hut

On one of the hundreds of flying earthmotes lives the Olcrid Metroshka and her host of hags and fiends. From this massive hut - with hundreds of rooms and workshops - her minions brew poisons and plot ways of overthrowing other powerful denizens of the plane. This hut is a hive of distrust and deceit, and even those inhabitants who have known each other for centuries guard information closely and lie to each other for no reason.

Type

Dimensional plane