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 trivia item below may give away important plot points.
After The Girl talks to the old man for the last time, as she looks off into the sky, a small U.F.O. hovers across and zips off quickly. It has been said that the U.F.O was actually a time machine that Kyun-woo, as an old man, used to revisit his past. The old man also made a brief appearance near the beginning of the film, when Kyun-woo and The Girl meet for the first time.