There are a few MegaDungeons on the isles. These are dungeons immense that can be visited time and time again. They are always an option for adventure. Those discovered thus far will be listed here for reference.
Maze of the Blue Medusa
You can enter the maze by visiting Polk in Izuz and using the painting of False Chanterelle to be magically transported into the maze. Inside, you'll find all manner of weird and magical creatures and characters. There's also many objects of value for the intrepid adventurer seeking to increase their fame, glory, and power.