Devil's Island
I'm not familiar with the history of the Penal Colony, so I might be way off. But Devil's Island didn't seem all that bad, compared to the solitary confinement section. At least you can grow tomatos, and not try to catch roaches....
And a question. Why was Papillon sent to the island? Is it because it was supposed to be really had to escape from, or because he was old by that point?