The Adventure Seed
In a Victorian-Era Campaign: Explorers trying to cross Greenland find an inexplicable temperate region, like an oasis or green in the icecap, hidden behind a region of fog. The region is inhabited by a variety of creatures long thought to be extinct, including a tribe of Neanderthals, who worship a strange race of unknown gods.
The "gods" of these primitives are actually an race of aliens who created this area as a preserve to hold biological specimens, but who never returned.
Will the explorers find the alien technology that maintains the region's climate? What other tech will they discover? Will the primitives start worshiping them? Or try to kill them? And what if the aliens come back?