A Peace Pagoda is a Buddhist stupa. It is designed to inspire peace and to help unite people of all races and creeds in their search for world peace. Most peace pagodas built since World War II have been built under the guidance of Nichidatsu Fujii, a Buddhist monk from Japan and founder of the Nipponzan-Myohoji Buddhist Order. Fujii was greatly inspired by his meeting with Mahatma Gandhi in 1931 and decided to devote his life to promoting non-violence. In 1947, he began constructing Peace Pagodas as shrines to World peace.
The Tokyo Peace Pagoda was inaugurated in August 1974 at the summit of Mount Odera (大寺山; 960m) near Lake Okutama. Not sure why or when it was abandoned. I had a first glimpse of the pagoda when I went to Mount Gozen a few weeks ago and I had no idea what it was: It seemed like a large structure (actually 45m in height and 55m of diameter) but there was no mention of it on maps or tourism pamphlets. So I went to see for myself after I got down from Mount Mito. The trail starts between Mito Bridge and Miyama Bridge. It takes about 50min to the summit.
Above, the view of the Peace Pagoda when exiting the forest trail. Although it looks like something a UFO cult would dream up, the architecture seems to have been inspired by the Peace Pagoda at Dhauli Hill, in India.
Above, one of the statues depicting the four stages of enlightenment of buddhism.
Above, view of Lake Okutama.
I looked for a door to get inside the pagoda but I could not find it. This page (in Japanese) has some info and photos.