Im having the same problem...stuck on top of the castle inside the wolfskull ruins cave, next to some circular altar, trying to find a way to lower the bridge. If I go back there's a point where i jumped down into the ruins section and cant get back up. Someone help pls

Read this:
www gamespot com /features /the- elder -scrolls -v -skyrim -walkthrough -6345388/? page=12

"Edit - having spent hours looking around i found there was a lever right next to the wooden bridge thats raised...just concealed by the darkness"

Thanx heaps, I was going bonkers

I've found this with some of the Dungeons, the most obvious route isn't always the right one. Check behind you occasionally lol.

When you first enter Wolfskull...make sure you have clear inventory. You will complete the first half of the dungeon, the upper level. Then you will drop down. Once you drop down you cannot go back out that exit. Clear the entire dungeon..it's pretty long. At some point you will reach a winding tower, followed by a circular chamber that is surrounding by 3-4 necromancers, and an elite necromantic matron (or something). Once they all die, get everything in that room and follow the circle area to the other side, the exit is there. Once you exit, you can then enter from either side. You can go in the original entrance, or this new entrance you just discovered.

Most longer dungeons have a back exit so you dont need to backtrack all the way back to an entrance.

Seriously, some of these answers aren't even for the correct cave/ruins.

Wolf skull exit:
At the sacrificial altar, there is a bridge across to a chest. On the right of the chest is a stairway down, leads you to entrance, as long as you stay out of the drop down areas, you will find the exit.

Sweetsensi has the answer. On the wooden platform in front of the bridge there is a lever, its hard to spot in the darkness but if youve killed everyone equip a torch or a light spell.

Retrace your steps.

Enter through the arched tower opening, ull hear a ritual in progress, kill all the followers and master, then pull the lever , it drops a wooden bridge to the next tower, i think theres a chest there as well, then head down and look for a door exiting back to wolfskull passage, check your map if u need to, then look down and jump next to the cart and u should be home free