Catalyst: Lejentia Campaign Book 2 - Fort Bevits

Subtitled: Adventures on the Dark Side of the River Styrmm
"Filled with villains, dark elves, and insectoid alien creatures called Novilles, Fort Bevits is a fully described fortress and caverns, with over 50 illustrated NPCs, 71 detailed scenarios, and over 20 maps of the fort and surrounding territory. Plus a 40-page intro section which details the politics, powers and culture of the Tarin Tor army."
publisher's description
Catalyst is a series of fantasy role-playing game supplements created by Flying Buffalo as a series of game aides that could be used with any medieval fantasy-themed role-playing game system. The first supplement, Grimtooth's Traps, was released in 1981.