There are lots of ways to have fun, some centering on the Yamanote, Tokyo's more-or-less circular commuter line. Few remember that not so long ago it was known as the Yamate Line and there was great consternation when the name was changed. From the beginning, people tended to speak of inside and outside the Yamanote. Inside, you were in the sophisticated city, outside you were in the rice fields (now called "bed towns"). It was intimated that you didn't matter quite as much if you were literally on the other side of the tracks. Still, it remains a convenient way of designating which side of the station you have chosen as a meeting place.
Now we come to the fun part. A reader has heard of a group that hikes around the Yamanote. He would like to join.
How about the Nihon Aruke Aruke Kyokai, a club for walkers inspired by five Japanese college students who walked from San Francisco to Washington, D.C. in 1963. The next year was the year of the Tokyo Olympics and all the wonders it entailed, among them the shinkansen, the Hotel Okura and Kenzo Tange's dramatic swimming and volleyball venues, which can still be admired near Harajuku Station. Japan's new wealth had not yet trickled down to college students, so a group of them decided to organize a walk around the outside of all the game facilities since they could not afford tickets to go inside, a mini-version of the U.S. walk. This included yacht facilities at Enoshima and other distant sites, so it was more than a stroll. That was the beginning of what is now a national association that promotes walking as a wholesome sport that everyone can participate in at any time or place without divisive emphasis on competition.