Never been to prison and hope I never will experience prison but I bet it's boring as all hell.
However some prisoners do get to go outside and play basketball on the yard or other games or workout and some prisoners do get to work on jobs which earn them good time credit which can help aid in their early release from prison.
Some play card games, mentor other prisoners etc and I've heard on some Prison Documentaries that some prisoners adjust to the prison routine and after the first 2 years or so time doesn't seem as slow as they're more occupied.
However I would still think that time would drag on.
Right now it's very cold and windy outside and I'm stuck inside the house and I feel trapped and like a prisoner and even though I have a computer and access to the internet and can walk outside anytime It still get to me.
I doubt I could cope with being locked up in prison for years but some people are able to get through it because they really have no other choice.