Like all catacomb levels, it's dark, cramped, and somewhat confusing to the inexperienced.
This level features the generated Chamber of Bone quest, which awards the Guardian spell, or raises it by one level if the character already possesses it, along with a few magical items in chests. Also, lots of undead are to be found, as expected; Horror Captains, to be exact. It takes place in a split level; unlocked when Mythical Book on the same level is read.
It's good to know that opening the middle door of the Chamber of Bone usually yields in an entire room filled to the absolute brim with Horror Captains. Past that are some Horned Demons ready to charge you in a rather open area, guarding a... well, guardian spellbook. It should be read while the enemies are distracted. Reading it automatically summons a Hydra to breath Firebolt at the players foes, but only for a limited time.
The following monsters can be found in Level 6: