Hey, c'mon, vote for your favorite beach! Only two people?!?
Anyway, some of the bigger festivals in the area:
Gwangju Biennale (September 5 - November 9)* Massive art festival held every two years in Gwangju, in and around the Biennale Hall on the north side of town.
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Official site.
Jeonju Sori Festival (September 26 to October 4)* Festival about traditional Korean music, in Jeonju, Jeollabuk-do.
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Official siteJinju Lantern Festival (October 1 - 12)* At Jinju, Gyeongsangnam-do. Absolutely beautiful festival in a beautiful city, a short walk from the bus terminal. A must-visit.
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Official siteNamdo Food Festival (October 9 to 13)* At Nagan Folk Village in Suncheon. Take city buses 63 or 68.
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Official siteGwangju Kimchi Festival (October 15 to 19)* Dedicated to Korea's representative side dish. As a foreigner prepared to be a spectacle yourself.
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Official siteJangseong Baekyang Maple Festival (November 1 and 2)* At and around Baekyangsa temple in Jangseong county, the temple a lot of Jeollanam-do public school teachers visited during Orientation. Popular spot for viewing the fall foliage.
Here's a more complete list featuring other festivals in the neighborhood and more detailed information. Please add your own if you know of any.