A One-Round Living Greyhawk Principality of Ulek Regional Adventure
From the introduction:
The Derro have plagued Urgo's Mine and the surrounding areas in the Lortmil Hills for years. Now it's time to put an end to the threat for good.
A Principality of Ulek regional adventure for APLs 4-12, and Part 5 and the finale of the Downward series.
Note: This adventure will be of particular interest to Mine Rangers and longtime PCs of the Principality of Ulek.