When most people think of Yamanashi the places that come to mind are the Southern Alps, the Fuji Five-Lakes area, Mt. Fuji, fruit farms, and wineries. However, one of the most popular day-hike trails within a couple of hours commute time from Tokyo is also located in Yamanashi. For a very scenic day hike, visit Nishizawa Keikoku (Nishizawa Gorge).
The round trip hike from the parking lot (or bus stop) is about 12 kilometers and takes about four hours depending on your own speed and the speed of the people in front of you. This is a popular hiking trail and gets quite busy on the weekends, especially during the autumn months when the foliage is changing to fall colors. The first half of the hike is mainly an upward climb, with a few flat areas, and takes you along the Fuefuki river and past several waterfalls. The hike to the top takes a bit over half the total time and you'll find yourself hiking along a dirt trail, rocks, manmade steps, and a couple of bridges across the river. Watch for signs along that way that point out some rocks that, when viewed from the right angle, suggest the shape of certain animals, such as "kaeru ishi" (frog rock).
It's not a particularly arduous hike, but there are places where you'll be glad to have the cables that are attached to the rocks as you use them to pull yourself up and over some of the rocks and steeper parts of the trail. If you take children along make sure they understand that the hike, like any hike, can be dangerous. You don't want them slipping on the rocks and sliding under the rope for what could be a long drop down to the cold river water. Also, it's a good idea to wear sturdy hiking shoes as some places along the trail are covered in loose gravel, or slippery from the water running off the valley's wooded walls. If you have hiking poles take them along; and a pair of those ever popular Japanese work gloves known as "gunte" (available in hardware stores or most any convenience mart) can save your hands from nicks or bruises as you clamber over rocks or use the cables and chains along the trail to keep you from falling.
Roughly 90 minutes from the trailhead (closer to two hours from the parking lot) you'll come to the 5 tiered waterfall named Nanatsugama-Godan-no-Taki, which roughly translates to 7 iron pots-five steps. It's possible to climb down and over the rocks to get closer to the waterfall for a picnic stop. There are other spots along the trail where it's possible to stop and have lunch or a snack break as you admire the scenery. However, most people continue to the top of the trail where there are a few rough hewn benches and a wooden platform where you can sit and have the picnic lunch you've brought along. There is also a toilet here and it's the only one since just before the trailhead. Be sure to bring along bottles of water, too, as there is no place to get water along the hike.
Keep going after the top of the trail and once you cross the river the way down is just an easy walk through the forest along a well packed smooth path that is more of a road than it is a trail. Take note of the steel rails that are along parts of the path and in some places jutting out into space over steep drop offs. In days past these rails were used for flatcars to haul the cut timber down from the mountain. The flatcars were pulled up the mountain by horses and the loggers would load the trimmed logs on the cars for the ride down the mountain where the logs could be dumped into the river to be floated on down to the mills. As you walk down you'll see one of the flatcars with logs stacked on it depicting what they looked like long ago.
If you decide to make it an overnight trip there are numerous Japanese inns along route 140 within an hour or so drive from Nishizawa Gorge.