The Kaihōgyō is a 1000-day pilgrimage around Mount Hiei, which takes seven years to complete on foot.
It is a ritual performed by monks, or gyoja, in the Tendai sect. The journey is equivalent to a trip around the globe and is traditionally seen as a way for monks to offer prayers to the Buddhas and for the well-being of others.
Only 46 monks have survived the ritual since it began in 1885, and those who are unable to complete it are expected to take their own lives.
The actual 1000 days are never reached, as the physical training is stopped just before that point, and the remainder of the days is spent trying to fulfill the unfinished task.
The purpose of the Kaihōgyō is not just the physical effort, but rather to offer prayers and seek enlightenment.
It is similar to an athlete setting a record and continually striving to improve upon it, but instead of a score, the goal is to find inner light and enlightenment.