Tales of the Fourth Age
Located on an island in the frigid Northern Sea, the Under-Gate is the largest known entrance to to the mysterious Underdark. The reclusive Drow guard the entrance against those who would enter, allowing only the occasional traders, ambassadors, and adventurers to enter.
Across the entrance to the cave stretch the massive and ancient Obsidian Gates, a relic of the Golden Age. Little is known of this massive construction as the Drow have not allowed any outside researchers to examine them. The only thing known for certain is that they have successfully and effortlessly repulsed all assaults launched against them.