Diablo/Chamber of Bone

Catacumbs level 6, find and read the Mythical Book. That will talk about the Chamber of Bone and it's minions, death and other stuves.

Find the entrance here at level 6. Enter it if you want to. Firstly, there is nothing that important here. It's just a chamber with some demons (specially squeletons) and rewards. Only good for experience and profits.

Go exploring the chamber and activating the levers to open secret rooms. Kill the monsters and go getting your rewards. Luckily you may find some unique or magical items that you can use or either sell for money.