it's the same thing. nothing changes. >> 90% of prison life is actually boredom. and it's what the inmates do with this down time, this lack of stimuli, that has led to some of the most interesting parts about lockup. >> you do your time. don't let it do you. >> the monotonous grind of life in prison can push some inmates to the limit. in trying to understand how they deal with the specter of never being free again, we've met some of our most memorable characters and recorded some of our most dramatic footage. >> i'm serving a life without parole sentence, two life sentences, two 99-year sentences, a 40-year sentence, a 20-year sentence, and a 10-year sentence, all together. >> at the time of our visit bobby gilbert had been at