National Foundation Day, known as Gaecheonjeol in South Korea, is an important public holiday that commemorates the legendary formation of the first Korean state of Gojoseon in 2333 B.C by Dangun Wanggeom. Celebrated annually on October 3, this grand event symbolizes the birth of the nation and its history. The term 'Gaecheonjeol' translates to 'Heaven-opened Day', befitting the mythology that credits the founding of Korea to divine intervention.

On this day, various ceremonial events are held nationwide in South Korea. One of the major ceremonies takes place at the top of Manisan Mountain in Ganghwa Island where, according to legend, Dangun ascended to heaven. Citizens do hike up the mountain as a remembrance to this legend. Other events include reenactments of the ceremonies performed in the ancient times, traditional music performances, and exhibitions of traditional Korean art and culture.

National Foundation Day is a platform for instilling patriotism and national pride among the Koreans. Apart from participating in the public celebrations, Koreans also spend the day visiting family and friends and having meals together. The holiday is an embodiment of unity and solid nationalism among the citizens of South Korea. Overall, Gaecheonjeol is not just a celebration of the nation's founding but also a day to appreciate the rich cultural heritage and history of South Korea.