Holmesburg Prison, built in 1896, closed in 1995, Philadelphia, Pennsylvania. This facility was the site of some dermatological, pharmaceutical and biochemical weapons research projects involving testing on inmates.
A top secret prison and labor camp on Goli Otok (Barren Island), now in Croatia. The uninhabited island was made into a high-security, secret prison for political prisoners, used between 1949 and 1956 by the Yugoslavian government.
I've been on a tour of the Eastern State Penitentiary. It is very creepy. Built back when they were all about putting the penitent into penitentiary. Photos don't really do it justice. It's total seclusion in the older wings. No cellmate, food slipped in through slits in the doors, and each cell had it's own tiny courtyard so prisoners never had any excuse to leave the cell or see or speak to another person.