From:
http://www.seoulfriendshipfair.org/
and
http://www.chrisinsouthkorea.com/2011/05/may-2011-events/

May 7-8 (12pm-8:30pm): Make some new chingu at the Seoul Friendship Fair. While the official offerings are everything from performances and art to street events, the World Food Court is perhaps the best reason to go. Don’t even think about eating before you come – there are dozens of food trucks, each offering respective country’s delicacies. Alcohol from around the world is around to help you wash it down as well. Seoul Plaza (i.e. that big piece of grass in front of City Hall).