Kagrenzel

Background
To reach Kagranzel, travel eastward up the steep hill near Ansilvund. Kagranzel will eventually be near the far east end of the map, roughly parallel with Stony Creek Cave. It appears to be something of an easter egg. Past the entrance is a room dominated by a mysterious orb on a podium. A couple of dead bandits lie near it. You can activate the orb which sends a circular gate up and starts the orb revolving around the gate. After a time, the floor under the gate shifts and spills you down a very long shaft, and eventually into an underground lake, with water cascading down from many places.

Bugs

 * You are able to get to the beginning of Kagrenzel from the lake, if you go through a glitch in the map past the locked expert chest, through an opening in between two rocks then keep swimming down. Make sure you are able to breathe for quite sometime here. Once you exit the map you will be placed in front of the entrance. (Tested a few times over Xbox)(Also tested on PC and possible without using underwater breathing enhancer)
 * It's possible for the player to die, if you drop down into the hole. If you get hit by one of the vases lying on the floor during freefall, it's an instant kill, even when wearing daedric legendary armor.
 * In Stony Creek Cave, climb the wall opposite the falls and using the Whirlwind Sprint, it is possible to enter through the exit into the ruins.