Theres a mod for Fallout 3/New Vegas that adds a Tunnel from game to game. Basically, you can start in Fallout 3, go to New Vegas, come back to 3, beat New Vegas, and back to 3...
Anyways, thought it would be cool if there was a mod similar to this for Oblivion/Skyrim. Obviously it would be awkward, sense the graphics arent the same, but the concept is cool.