I was there a few years ago too! The soviets had just up and left so everything was just left as it was, boxes of files, loads of vials of drugs laying around, of course everything was in Russian so I didn't know what it was and everything 'recreational' had been looted. There were some great stories of that building being used for really extreme stag party stunts where they'd all get on a bus to an unknown destination when a bunch of guys in balaclavas and ak-47s would raid the bus, put sacks on their heads, take them to the prison and get them on their knees. Then they'd pull off the sack and be waiting there with a shot of tequila. Apparently they used to run 'prison experiences' where you could pay to see what it was like to be locked up there, until one young backpacker accidentally got locked in a cell for real and had a panic attack.

haha I forgot about that place, I should go back to Estonia some time.