Japanese love trekking and hiking. On the other hand, many foreigners think that Japan is covered by asphalts and concretes and there are few natures. Hokkaido is full of nature and Honshu too.
May be the most famous place for trekking for people living in Tokyo metropolitan area is Oze national park. Oze national park, seceded from Nikko national park in 2007 to become the 29th national park of Japan, is located in 4 prefectures, Gunma, Fukushima, Tochigi and Niigata. Actually, the area belonging to Gunma and Fukushima is more than 90 percent of whole area of Oze national park.
Then, if you see a word Fukushima, you will try to avoid going there. However, Fukushima prefecture is not a small area. Its area is 13,783.74 km2 which is almost 1/3 of whole area of Switzerland. It is more than 200 km away from Fukushima Dai-ichi nuclear power plant.
Unfortunately Oze national park does not have any JR station nearby. Major routes are taking buses from Tokyo or taking a night train from Tobu Asakusa station in Tokyo to Aizu Kogen Oze-guchi of Yagan railway. Then, you can change to local bus to Numayama pass of Oze national park.
Private vehicles and buses are prohibited to enter the designated main area of the national park, therefore you have take share ride taxis to reach the entrances of the park. Many hikers and tourists visit the national park during the season of a flower, Asian skunk cabbage.