Seoul is a perfect city for a few days stopover. I absolutely love living here, but I can say as a tourist, a long weekend like Thursday to Monday, or a few days during the week is ample. Day trip to the DMZ, spend a day in Myeongdong/Jongno/palaces, a day in Gangnam, go out at night. Seoul ABSOLUTELY shines in the food and nightlife department. I can honestly say it's the best nightlife in Asia. Nowhere else has come close for me yet!