Almost all sinners and evil people end up here.

The River: that flows from the Interstice into the Hells
The Gates: guarded by hellhounds and watched by other demons. Hunters have their headquarters here.
The Circles:

1. First Circle: the petty sins, called Sheol; it is possible to escape from here.
   
2. Second Circle: lust, called the Tempest.
   
3. Third Circle: gluttony, called the Bog.
   
4. Fourth Circle: greed, called the Lode.
   
5. Fifth Circle: anger, called the River Marsh; one of the cities is here.
   
6. Sixth Circle: heresy, called the Tombs.
   
7. Seventh Circle: violence, called the Rings.
   
8. Eighth Circle: fraud, called the Malebolge.
   
9. Ninth Circle: treachery, called the Lake of Ice.
   

The Palaces: home to many nobles and princes; there are 131 palaces.
The Cities: home to the free demons; there are 13 cities.
The Black Furnace: never complete, this great Furnace's function has changed over the Ages; few understand now what it is for.
The Lake of Fire: a lake that purifies the unrighteous before they are taken onward to punishments.
The Prison: a prison for those who try to escape, where crueler torments await.
The Forest: where zaqqum trees grow.