Tokyo Stock Exchange, Tokyo
Not many people knows you can visit Tokyo's stock exchange market building, for free!
It is not a remarcable touristic spot, but you can spend 30 minutes walking by the empty futuristic corridors, while brokers are "playing" from their homes and offices: yes, there's nobody inside, but a few stock controllers and the guys of some specialized TV chanels... It looks like that science-fiction films with a cold computer brain controlling their lives... but you'd better see it on your own!
I thought the Tokyo Stock Exchange was incredibly interesting. The Japanese day traders are certainly calmer than the ones you see on Wall Street. They have many nice exhibits and tools that help you learn about the stock market. Really cool!