Or more specifically, megadungeons. Are there any megadungeons who have played a significant role in fantasy (and/or any of its "offshoots") literature in the last twenty-five years?
The Mines of Moria are perhaps the most well-known example of a megadungeon in fiction. And while they are important to the Lord of the Rings as an obstacle to be overcome by or as a road to be traversed by the Fellowship or, if I remember correctly, as a means to separate Gandalf from the others, they don't play much of a role in the story. The time spent in their halls by that adventuring group (in words) isn't all that great compared to the entirety of the trilogy.
But are there any other examples of megadungeons in modern fiction? I'm interested and would really appreciate any other examples. Thanks!