When is National Foundation Day ?
This holiday is always celebrated on 3 October.
Also known as the "Festival of the Opening of Heaven", Tangun Day or Gaecheon-gol, Foundation Day commemorates the traditional founding of Korea by Tangun in 2333 B.C
Go-Joseon (also called Choson) or Old Korea (2333 - 206 BC), was the first Korean kingdom. According to legend, it was founded in southern Manchuria in the basins of the Liao and Taedong Rivers.
The legend goes that Prince Hwan-ung had left heaven to rule the earth. In the kingdom, there was a bear and a tiger who prayed to the prince that they wanted to become human. He said that if they stayed in a cave for 100 days only eating mugwort and garlic they would become human. The tiger got bored and left, but the bear completed the 100 days and became a beautiful woman. She and Hwan-ung bore a son called Tangun Wanggom, When Tangun grew up, he built a city at the present site of Pyongyang (now the capital of North Korea) and called his new kingdom Go-Joseon, meaning 'morning freshness'.
Judging from Chinese records, the state of Go-Joseon as a political entity could be described as a kingdom at least by the beginning of the 4th century BC. This roughly coincides with the advent of the Iron Age in Korea.
Go-Joseon went into a period of decline, but it was revived in the 2nd century BC as Wiman Joseon.
Some Korean records combine Wiman Joseon, Gija Joseon, and the initial Go-Joseon as periods of one Go-Joseon.
The holiday is celebrated with ceremonies on the summit of Mount Manisan on Kanghwa island, about 25 miles west of Seoul. This is where tradition says that Tangun offered sacrifices to heaven.