The trouble with epic level dungeons is that you need reasons why the players can't simply ignore doors/walls. An ordinary dungeon isn't going to cut it.
On the other hand, if a Prismatic Dragon were to be twisted by the Far Realm, taking on psuedonatural aspects, and started tunneling under the earth, boring into rock and encasing itself in a prismatic cocoon that leaks out into the walls, making the walls prismatic themselves, heading for the core of the world where it will begin devouring the divine spirit of the planet slowly over the course of a few centuries, bringing about a plague of mysterious death as the lifeforce is simply sucked out of all living things, granting liches/demiliches/akaliches access to an easy army of bodies with which to animate...
*gasps for air*
...which intrude on the borders of Fairyland, causing an interdimensional war between either Oberon or Mab or Titania and the lich(es) in question, with outposts inside the prismatic caverns twisting reality and perceptions, drawing out the LeShay from their eons long slumber and sending them into battle, all the while Asmodeus is getting worried that a major source of souls will not only be removed from the reach of hell, but is actually going to feed a being hostile to all existence as we know it, good and evil; so he's going to send forces in to attempt to slay the dragon, but without much success... and then the gods get involved in the chaos.
Well, that sounds like the beginnings of an epic dungeon. This only helps if you're willing to design the map yourself, of course. As far as published epic dungeon romps... I have no idea. Upper_Krust was in the middle of converting
The Bloodstone Throne into 3.5e, but that's designed for high-epic, not low epic.