I always wanted to make a "habitrail for an octopus," it looks like someone went and did it:

http://scienceblogs.com/pharyngula/2007/01/not_for_claustrophobics.php

Whoa. I especially like the way it changes direction to get out the hole in the side of the pipe. Awesome.
...I want to be an octopus.
(This board has the best smilies ever, incidentally. :pohlsepia)