Take the drive out to the west of Tokyo on the Chuo Expressway or catch the Chuo Line to Takao station from Shinjuku. Not only is this a lovely area with mountains and beautiful greeny but there is also a fun cable car which takes you most of the way up the mountain. When you get to the top there are fantastic views of Tokyo, a shrine, and an area where the kids can enter and hang out with the monkeys.

The monkey park has about 40 monkeys and there is a guided tour to teach you all about their social stucture. It costs to get in but not that much.