This film was based on a true story.
In 2010, a memorial was made around of the tree where The Girl and Kyun-woo buried a time capsule under it. The memorial is called "Time Capsule Park," and it was made in honor of the tenth anniversary of this film. The exact coordinates of Time Capsule Park are (37° 12' 05.60" N, 128° 41' 19.50" E).
The frog/toad Kyun-woo finds inside the time-capsule is a reference to Ol' Rip the Horned Toad, which is a toad supposedly came to life after opening the time capsule he was buried in for 31 years.
The name of Kyun-woo comes from the Chinese story of Qi Xi (Chilseok in Korean), where the Cowherd (Gyeon-wu) and and the Weaver Girl (Jiknyeo) of the heavens are united for only one night every year.
The exact coordinates of where The Girl and Kyun-woo yell at each other on hills are: The Girl: (35° 18' 48.75" N, 128° 58' 48.75" E) and Kyun-woo: (35° 18' 17.75" N, 128° 59' 45.75" E)