Its a big street with the monument of a general and the father of the korean alphabet.
Besides renowned for the King Sejong's statue and also the underground museum, I liked my visit to Gwanghwamun Square on a weekend when there was a flea market along the square. It had numerous to offer, including the delicate wooden craft that was attracted me. I also enjoyed watching various activities around the square. It looked like the Seoulites were enjoying the weekend spent there.
Huge central plaza in front of Gyeongbukgong Palace, and easily accessible through the city subway. Check out the statue of King Sejong at the middle of the square - there's an entrance at the back leading to an underground museum dedicated to the life and works of Sejong The Great.