You can see and even participate in fire walking at the Mt Takao Hiwatari Festival, held near Takaosan Yakuouin Temple. The sacred act of walking on hot coals and embers is regarded as an act of cleansing and purification, which, as well as being good for cold feet, also apparently promotes plenty of good stuff including world peace, longevity and health, prevention of disaster, and protection from road accidents. There are still some risks though: of two friends who tried it a few years back, one got across unscathed while the other got burnt feet!
The festivities are a short walk from Takaosanguchi Station on the Keio Takao Line from Shinjuku.Organizers may cancel events, alter schedules, or change admission requirements without notice. Always check official sites before heading to an event.