An excellent place to get a tiny taste of Sumo, the national sport of Japan, is to visit the morning practice of a sumo stable.
One place that is particularly convenient is Arashio stable, which has large windows into their practice room, and allows visitors to watch quietly from the outside. Please be respectful, and read the instructions carefully before visiting.
If you have good timing and happen to be visiting a city where the sumo tournament is taking place, definitely try to get tickets! Sumo is quite fascinating live. The speed and size of the sumo wrestlers really doesn't come across on TV.