Do not miss:
*The National Museum of Korea. Great building, great exhibition.
*The nearby Gyeongbokgung Palace
*Banpo Bridge Moonlight Fountain Show. between late April and the end of August at noon, 8pm, 8.30pm and 9pm Monday to Friday; and noon, 6pm, 7.30pm, 8pm, 8.30pm and 9pm on Saturday and Sunday.
*Street food, eg. at Gwangjang Market, founded in 1905 and one of the biggest food markets in Seoul.