Visited a prison for a psychology of criminal behavior class in college. Two main things I remember:
1. Getting a stamp on the back of my hand on the way in that only showed up under UV light, being told that if I didn't have that stamp on my way out I wasn't going anywhere, and spending the rest of the visit making sure I didn't touch the back of that hand and somehow rub that thing off.

2. The professor telling all the girls in class not to wear anything even slightly revealing on the trip. When we got there, it didn't seem to matter much what they were wearing (and the guys got about as many comments as the girls).
Oh, and the room where they have new inmates squat and cough - supposedly if you're smuggling something up your ass it's tough to keep it in there when doing so. Who knew?