Character: I must be getting close!
Hell is the fourth and final set of levels in Diablo I, consisting of levels 13-16. It looks more depressing and horrific than the other levels. There are corpses impaled through stakes, hanging on walls and walls made of bone with their interiors filled of pulsating blood.
Staircases appear like huge halves of ribcages.
Just like how every first level of a level set has a staircase up to town, so does Hell, and the entrance outside is a blood-red crevasse in the earth, behind Pepin's clinic. Mousing over it says "DOWN TO HELL."
Hell contains half of the multiplayer quests, as well as two singleplayer-only quests. One of the two (but never both) of the singleplayer quests will appear in each game.
In some game-instances, you will find the Warlord of Blood, whose room contains the ribcage-staircase to Level 14, and some racks where armor is displayed, as well as some weapon stands.
The entrance to level 16 says "DOWN TO DIABLO" and is a circled star with a hole in the center; it appears nothing like the other ribcage staircases. Upon entering Level 16, you will see a shadow of Diablo over the pentagram on the level loading screen.