Kaihōgyō is a very long and difficult religious practice that comes from Japan. It is done by some Buddhist monks who live in a special temple called Mount Hiei. These monks do a very hard form of training that lasts for 1,000 days! That's almost three years! During this time, they don't get to see their friends or family, and they only allow themselves to eat a small amount of food once a day.
The most difficult part of kaihōgyō is the final 100-day challenge. During these 100 days, the monk has to continuously walk or run for 52.4 miles (84 kilometers) each day! That's like walking from your home to the next town, and then doing it over and over again!
If the monk can complete the final 100-day challenge, they are considered to have achieved a very high level of spiritual enlightenment. People who have completed kaihōgyō are admired and respected in Japan for their dedication and perseverance.
In short, kaihōgyō is a very hard thing that some religious people in Japan do to show how dedicated they are to their beliefs. It involves training for almost three years and then walking or running for 100 days straight, covering more than 52 miles each day.