I went in through Stony Creek Cave and found the way in to Kagrenzel blocked by an impassable waterfall too high to jump up to. So I found a way outside to the entrance to the ruins. Once inside I was greeted by two dead bandits next to some kind of glowing orb. I had the option to touch the orb and immediately this metal cage slams down around me trapping me inside. Agonizing moments pass as strange sounds were heard, while I desperately looked for a way out.

Without warning, the floor drops out and I fall for what seems like 30 seconds down into this dark water filled cavern. I reminded me of blackreach with all the glowy specks on the ceiling. I made my way out finding the top of the waterfall I was unable to reach before. I killed a lot of falmer on the way.

I think that was the most scared I've ever been playing this game, and I just recently completed the main quest.