When walking up to the wall in the Ansilvund Excavation (for exact location see Dungeon map with location marker: image SkyrimBugs/1/ScreenShot4.jpg hosted on aladdin.aikebah.net)

The screen suddenly changes to a bright yellowish void with some distant dungeon parts (see image SkyrimBugs/1/ScreenShot3.jpg hosted on aladdin.aikebah.net)

This is probably not an Ansilvund issue but a general scene loading problem. Every once in a while there is a error in the load; I've seen it in exteriors and interiors. If you save and reload it should correct itself.