On March 26, 1991, five young boys set off for a day of fun together, catching frogs in the streams of Mount Wayong, South Korea as their country celebrated a public holiday.

But by the time the sun set, U Cheol-won, 13, Jo Ho-yeon, 12, Kim Yeong-gyu, 11, Park Chan-in, 10, and Kim Jong-sik, nine, had failed to return home.