That would be a nightmare of a dungeon, starts with a Zombie Dragon that's probably already high lvl, and then a spell is required to break through the endless loop of the next layer, and then ontop of that you have to be weary of the dozens of lesser undeads roaming, and finally the cream of the crop the outer gods spirits, ancient dragon spirit, and the wise man who summon them...
It's like you walk up and it's just lvl: Infinity Dungeon