The Catacombs continue underneath the Cathedral, and while the former is much darker, the layout of both areas is similar, as both have large rooms with narrow doorways that make for natural chokepoints. The Catacombs feature narrow corridors in addition to the doorways, and some rooms also have large openings rather than doors into them. Skill Books and Scrolls still spawn on these levels in small separate rooms.
Upon entering Level 5, the character mentions, "The smell of death surrounds me."
Zhar the Mad: A crazed Mage-type monster called Zhar the Mad stands in a small room which looks akin to a study. He will tell will first give the player a Skill Book and then tell him to go away. If the player touches the Bookcase in the room however, Zhar will attack.