Drepstan Dungeon

From long before Drepstan was razed to the ground, the settlement prioritised building a giantic underground city network. Regarded now as catacombs, or a vast dungeon, a sprawling subterranean cityscape, or simply the ruins of a possible civilisation. Almost entirely crumbling to pieces, the network of rooms and tunnels spread beneath the settlement of Drepstan, and possibly even further still. Some adventurers claim to have trekked miles in the caverns, to end up finding themselves back at the entrance - other adventurers not able to make such claims, as they've been lost to the labrynth. In recent decades, it's very rare to hear of anyone who has ventured in and come back out. What could lurk down there? Some evil vurse? A race of dungeon-dwellers? Or are the winding hallways and rooms just too difficult to traverse?