Ever had an overdue library book? I've had more than a couple in my time, and I'll admit there are a couple of libraries around the world who wouldn't be screaming to have me back.
So when I visited Estonia's second largest city, Tartu, and I heard that they used to lock up students for having overdue library books, I had to visit the place where it'd happened. In the top floor of Tartu University you can visit the student prison that used to house students who'd committed various "crimes" during their university studies, one of which was having overdue books. Inside the lock-up, bored and imprisoned students have decorated the walls with poems, pictures and cartoons - unfortunately some were damaged in a fire, but you can still get a fair bit of entertainment out of the visit.
And since then, I've sworn (again) not to have any overdue library books. If you need the same shock, check out my article on Tartu University's Sights and you can visit the lock-up for yourself.