In 1980, the Zushi Kaisei High School Mountaineering Club attempted a winter mountain climb in Happo-one, Nagano Prefecture, which ended tragically with all members dying.

This accident, which was caused by an immature plan that had been attempted only after a summer preview, and the extremely cold and harsh environment, shocked the whole country.

Furthermore, after the accident, a lawsuit over legal liability developed.

Why did such a tragedy occur? We provide an easy-to-understand explanation of the details, background, and lessons learned from the accident.