For the really Violent prisoners that are on lock down or in the hole or SHU whatever you want to call it then those prisoners in the hole will sometimes spend 24 hours per day in that cell with nothing but a toilet, bed and sink and nothing else to occupy their time.
Sometimes they'll be let out of the hole cell to shower and maybe get 30 minutes to an hour outside in a small cage and when they're moved outside that cell their feet and hands are shackled while moving them outside the cell and back.