One of the best places in Kanto to see Mt. Fuji is in Arakurayama Sengen Park, which has this famous view.
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...The park starts at the base of Mt. Arakurayama and goes all the way up the mountain. There is a viewing deck at the top of a 398-step climb that offers a view of Fujiyoshida City and the majestic Mt. Fuji in the distance. The park has a beautiful view that changes with the seasons. The spring sakura (cherry blossom) season is the best time to get the famous picture of Mt. Fuji, the cherry flowers, and the five-story pagoda.