The Wizardarium of Calabraxis
The Wizardarium of Calabraxis starts off with strangely behaving apemen, but players who start to explore the cave where they reside will soon discover there is a lot going on: ancient civilizations, the mad experiments of a forgotten wizard, and a couple unique magic items are guaranteed to provide a lot of bang for your buck to your players. This module has stats for the DCCRPG, but if one wants to work around the weird dice, this module is probably at home in just about any OSR rules system.