An octopus flooded the Santa Monica Pier Aquarium (note the link on the 2nd page to a video showing an octopus climbing through a very small hole- really cool if you haven't seen them in action before)!  And here's another take.

This reminds me of a story they told me at the Baltimore Aquarium on a behind the scenes tour.  Apparently their octopus had, several times, at night, climbed out of her tank and into the tank next door.  She would have a snack and then go back home before morning.  They didn't figure out where all the critters were disappearing to until they put a camera back there one night.  Then, they had to keep a cinder block on top of the octopus tank so she couldn't get out!

Another interesting fact they told me: most aquariums have a "backup octopus."  Why?  The ones in captivity are generally female, and when they "decide to" lay eggs (I don't know what prompts them to do it or if it can be detected before the event), they die very quickly.  So, a backup octopus is kept.  Interesting...