A few Suggestions if ever in Seoul:
1.) Absolutely visit the War Memorial Museum, not only enlightening but entertaining as well with reenactments.
2.) Itaewon is the most international district I visited in Seoul, however it is full of fun restaurants and bars. Go to the Grand Hyatt and look at the view over the city and eat some Ynang Num (sp) chicken at the their recommended spot down the street.
3.) Style watch in Myeong Dong. Great fashion made in Korea.
4.) Souvenir shop in Insadong. Make sure to pick up some Red Ginseng Tea and lacquer china with mother of pearl embellishments.