Or a fairly sizeable snake...or octopus...a chimp...predatory great cat...
(assuming you weigh about 200lbs)
Depending on the nature of the enclosure, those creatures have abilities that would make it easier for them to escape than a human.
Snakes can climb pretty well, and could probably slither through bars meant to contain humanoids. They're also decent swimmers. This would be a large boa or small anaconda or python.
Octopi can survive on land for brief periods of time (about 1/2 hour or so), and can squeeze through any opening larger than their beak...about the size of a quarter for most species. A great pacific octopus can be 200lbs, and something like 20' across, arm tip to arm tip. Even if he couldn't get through the bars entirely, he may be able to reach the keys...
A chimp is a much better climber, and pound for pound is much stronger than a human. A chimp may be able to bend prison bars just enough to escape.
A great cat could make jumps that Olympic jumpers couldn't hope to match- from a standing position, mountain lions (@180 lbs) can jump a vertical distance of up to 15 feet and a horizontal distance of 40 feet. They are also fast and quiet.