Even landing outside the play area, you should still see walls, etc. Does the minimap show your location in the room, or outside?
It sounds like one of the files in the save folder may have become corrupt.
Try deleting the files in the dynamic folders;
'..\Beyond Divinity\Acts\Act1\Dynamic', '..\Beyond Divinity\Acts\Act2\Dynamic', etc.
These folders are used as a cache for the game. Files are created / copied there from the save game folder when you load, and written / copied to those folders when you save a game. The files will be re-created as required the next time you start Beyond Divinity. If there was a corrupt file in those folders, deleting the files should fix the problem.
After that load a save before jumping down the pit and try again.
Two other people have had this problem on this level, but after going though it and then returning later. I'll find a save at that point to get a known good file, in case deleting the files in the dynamic folders and reloading a recent save do not help.
