Canon:Demonweb Pits

The Demonweb Pits is the 66th layer of the chaotic evil-aligned plane known as the Abyss. As a result of the popularity of Drow (Dark elves), in both the game and the supporting novels, it continues to be one of the best known layers by both players and authors, and was featured as the setting of the grand conclusion of a series of adventure modules in the early years of the game (see below).

The layer is the home of evil drow deity Lolth, the Demon Queen of Spiders and many other deities of the Drow pantheon of gods. The plane resembles a giant spiderweb across space, formed from strands of interwoven planar matter. Lolth's palace is a giant iron stronghold stylized in the shape of a spider, that crawls across the web strands of the plane.

The 1980 1st-Edition AD&D module Queen of the Demonweb Pits describes the Demonweb Pits as an environment quite unlike the Prime Material Plane, stating that many magical spells and effects do not function as expected here. The web strands themselves are reported to be composed from the lost souls of the Abyss, surrounded by a grey foul-smelling fog above and to the sides of each strand, forming a tunnel-like structure.

In Forgotten Realms
In the 3rd-Edition Forgotten Realms campaign setting the Demonweb Pits exists as a plane separate from the Abyss, due to the events of The War of the Spider Queen. The Demonweb Pits is still a layer of the Abyss outside the Forgotten Realms cosmology.