After finishing the main quest, the walls of the Temple of the One do not exist. They are not in their ruined state, there are simply not there.

http://cloud-2.steampowered.com/ugc/576738944345702621/362CCD62A31B350FFD195FCBCCC376888FC58460/

Also, when inside the Temple, it appears to be lower. The doors to the other districts are actually above the ruins of the walls.

I'm using the Unofficial Oblivion Patch.

Load order