I recommend this kind of festival, you will meet real stuff of KOREA.
This Festival is about Culture of the kingdom, It called Baekje.
The kingdom of Baekje has 678 years history.
Explanation of Baekje is not easy for me, If you visit public website of the Hanseong Baekju Cultural Festival, you can find more detail about Baekje.
Take subway line 5, get off Olympic Park station, exit Number 3, you will reach the Olympic park, and join, enjoy Festival.