The Nine Hells of Baator is an enormous plane of existence, and the origin of Devils in Dungeons & Dragons.
Avernus is the first layer of the Nine Hells and is the main battleground of the Blood war, ruled by Zariel. Avernus is the only layer of the Hells that can be accessed by planar portals. It is covered in ruins and jagged rocks. Toxic gas and a fiery red sky make up this atmosphere.
Dis is a barren landscape with filthy rivers and hills. Dis has a dull green sky with clouds and lightning. Ruins also dot the area from a time when the Blood war reached Dis.