Here are some ideas for dungeons i have that might be useful. Feel free to add your own.
Library of Dusk : Lower Vault (dungeon)
you all comes down a long stairwell that leads to a large room surrounded by smaller catacombs. In the middle of the room is a large caged off area with a sign over saying that only 2 may enter. Two enter here and the timer starts and the other two must search for the proper sequence of books. Opening the wrong book spawns mobs and/or bosses in the cage which the other two players must deal with. Some books switch players in and out of the cage, teleport you around, spawn chests, weaken the boss, strengthen the boss, activate traps, deactivate traps etc. The catacombs are also infested and have roamer mini bosses for added chaos.
You have to find the proper sequence of books from the catacombs before the timer runs out to open the cage and spawn the last boss. The location of the books is random every time the dungeon loads.
Ancient Dwemer Labyrinth (dungeon)
the ruins are full of levers and traps that trigger moving walls and patterned moving walls. Roaming the hallways are shielded dwemer automations. There are two ways to defeat the automations. 1) deactivate the power core and then kill them(someone would have to stealth ahead and do this or fight your way there). 2) trap them in the moving walls/pit traps. There are traps in this dungeon where if you die you cannot be resurrected and are dismissed from the group. The bosses are not difficult with a full group but getting to the boss with a full group is.
Worldboss Challenge Rampage
You have to kill a number of Random worldbosses from anywhere in the world in a limited time. Doing this within the timeframe allotted opens up the final destination where you face the final boss with whatever time you have left. When time runs out its over.
We shall know them by their works.