The main world for this minigame/skill is world 77.
The current active FC's to join to buy floors or hire advanced players:
Dghub, Keyers FC, Dg service
If you are already high level but are returning after a long time away, we recommend you running at least 1 or 2 floors first with these FCs on full screen mode and zoom out to Modern camera settings to maximize your view of the floor, so you can watch the advanced players dungeon at full efficiency. It should help you warm up for rushes and later, full groups.