Mt. Mihara Mountain Marathon (三原山マウンテンマラソン)

The Mt. Mihara Mountain Marathon is a navigation event on Izu Oshima, run as a smaller companion to the Izu Oshima Rogaining the day before. Reception, start and finish are at the Mt. Mihara summit entrance rest shelter, and competitors carry a map and compass around an area limited to Mt. Mihara and the Omote and Ura Sabaku desert zones, with a three-hour time limit.
Two formats are offered: Straight, where checkpoints are visited in order, and Score, where they can be collected in any order within the time limit. Entry is open to solo competitors or teams of two to five, all aged 18 or over, and team entry costs 4,000 yen per person.
The terrain sits on a volcano with striking lava landforms and sea views from the mountain, but it has few clear paths and many subtle landforms, and it is known as one of the most demanding navigation settings in Japan. It also hosts the Geopark Oshima Orienteering Meet, which is not being held this year. Maps are based on Geospatial Information Authority of Japan topographic sheets rather than special orienteering maps, and the courses are set by top orienteer Shigeyuki Koizumi, who also produces maps for the Izu Oshima Rogaining and the OMM. He has prepared checkpoints somewhat harder than those of the previous day's event.