 An engraving of this plan is found on a brass plaque just inside the facility's double-gated airlock-type main entrance.The prison's two current Restricted Housing Units (RHU) are essentially prisons within a prison and house over 300 prisoners — about 10 percent of the total prison population - who are allowed one hour a day for exercise, remaining confined to their cells the other 23, where they receive three meals a day and are permitted shower visits.The prisoners in RHU are allowed only one visitor per month.