October 3 is National Foundation Day in Korea, celebrating the creation of the country in 2333 BC.
This country, often called Gojoseon (ancient Korea) to distinguish it from the later Joseon Dynasty, was located on the northern part of the Korean peninsula where North Korea is today.
Dangun Wanggeom is the legendary founder of Korea. The foundation myth says that Dangun was a descendant of the gods. I won’t recount the entire story here, but you can find it all over the Web. Just do a search for Dangun or Tangun or Korean founding myth.
The oldest existing record of this founding myth appears in the Samguk Yusa, a 13th-century collection of legends and stories.
A good way to commemorate this holiday is to read the story of Dangun. I’ve also seen a cookie cutter in the shape of the Korean peninsula, and although I don’t have it (yet) making Korea-shaped cookies sounds like a fun activity for the day.