The Lost City (2003)

From the Back of the Book:

The Lost City is a fully developed location sourcebook for the d20 post-apocalyptic role-playing game, Darwin's World. Designed for starting characters, The Lost City details in full the legendary "Sunken City", formerly Bakersfield, California, as described briefly in the Darwin's World Gazetteer, at the foot of the Great Rift Vally.

A party of four to six characters of level 1-3 should be able to meet and deal with the initial dangers of the Lost City, but later dangers will require characters of much greater levels. The very nature of the city permits characters to carve out a niche or base of operations; permitting a protracted campaign to explore the city and encounter its bizarre troglodilian peoples.