Old, small, friendly gym in the basement below a small climbing shop. There's a foreigner there, and if you're in the region, this is probably the place to be. Akdong has been around since 1991? and is the creative force behind the bulk of the climbs at Yongseo Falls.
From Gwangyang station, cross the street (use the crosswalk to th S-Oil) and head left. . . a few tens of meters. Use the door left of the climbing shop (or browse the shop first).