Gehenna

Gehenna is an outer plane that bordered between lawful evil and neutrality.
Gehenna is a plane that consists of four layers that all share a couple of similarities. The first and most obvious is that although upon entering you would be standing on flat ground, the entirety of all four infinite layers feel as though there is a slant to them, as if you were standing on the side of a steep mountain. If one was to lose their composure and lose their footing, they would fall and tumble for miles on miles before something would catch them giving them enough leverage to stop themselves. This is assuming that they didn't fall into one of the many steaming rivers, boiling mud pits, and lava flows first. The heat from each layer comes from the ground itself, steam vents, erupting volcanoes, earthquakes that tear up the land making new lava flows are all quite common here. As such, there is a constant stream of smoke and steam that flows up into the dark void that is the sky. Any type of community, civilization, or building has to be carved into the ground or there would be no way of making it stand. Portals from one layer to the next are far and few between but are most commonly found in tunnels that lead underground which seemingly led to a dead end.
Khalas
Khalas is the first and most livable layer of the plane. The layer is solely lit with a dull red from the constant flow of lava. Numerous waterfalls also flow down the slopes and as the water evaporates due to the intense heat, mixed with the erupting volcanoes, the air is filled with a thick layer of steam and smoke while the ground is covered with a warm ash. The river Styx also flowed through this top layer and it was especially violent in this plane with harsh rapids that would crash into the sides of volcanoes before flowing underneath them.
Chamada
Chamada is the second and most active layer of the plane. Active in the sense of violent earthquakes and angry volcanoes. Solid land was actually hard to come by even in this infinite layer. City sized volcanoes would spew out fast flowing oceans of lava that were hundreds of miles across. The air so thick with smoke that it would kill the unprotected lungs and permanently blind the unprotected eyes.
Mungoth
Mungoth is known as the cold layer of Gehenna. There are far less volcanoes and most of them are much less active than the other layers. The flowing rivers of lava are much cooler, the steaming vents that spew ash less frequent, but the layer is covered in a mixture of snow and ash. This mixture creates a very muddy surface on the ground that makes it even more likely that you will slip, fall, and never find purchase to catch yourself.
Krangath
Krangath is the final layer and it is the deadest in every sense of the word. The volcanoes have been dormant for millennia, there is no ash on the ground or smoke in the air. Without any source of light made by the visitor, the layer is completely void of light and you would be able to see someone else's light from a hundred miles away. The air is still, dry, and freezing cold with no wind flow other than the slightest of breezes when a new portal opens and closes. The ground is covered in a thick layer of a glass like surface, paired with the heavy slope that permeates through the whole layer makes it extremely difficult to keep a foot hold or take a single step.