The dark cave wherein live Dragons, Drow, the Undead, and all other monsters with their own sourcebooks.

Drow of the Underdark*

Elder Evils

Exemplars of Evil*

Fiendish Codex I *

Fiendish Codex II*

Lords of Madness*

Libris Mortis

Draconomicon

Fiend Folio

Asterix (*) indicates a book not currently at our disposal.