This is a completely customizable LEGO marble maze designed by Jason A. that features interchangeable playfields (including a medieval themed one!). It's currently a LEGO CUUSOO project, so if it gets over 10,000 votes LEGO will consider making the set a reality. Honestly, of all the sets on the site that wouldn't require obtaining any licensing rights, it's definitely one of the best I've seen. Of course I don't really troll the CUUSOO site looking at other designs either, so it might also be the only one I've ever seen. Remember: everything is relative. My best friend is also my worst friend (because he's my only one).
Hit the jump for a couple more shots of different playfields and a video of them all in action.
Thanks Jason, and keep up the good work (read: make some dino and space-themed mazes).