The Museum of Criminology in the main campus of Meiji University in Ochanomizu, Tokyo has displays of policing in Japan and torture devices from around the world. It’s free and is a good place to spend 30 minutes to an hour if you’re in the area.
This exhibit shows an old Japanese torture technique. If you’ve ever done a traditional Japanese art and sat in seiza for an hour or so, you can imagine how painful this must be. I think I’d choose waterboarding any day.