From Oncheonjang Station, cross the pedestrian bridge to HomePlus. The street behind HomePlus is Jangjeonno (장전로) you're heading right about one block to the first big street: Sikmurwon (식물완길) and head left (towards Geumjeong Mountain). Go two blocks-- on your left will be 온천화목, on your right, a duck-soup restaurant 장수오리탕. Head right at the duck restaurant . . . a few places down you'll see the onsight sign. Follow the arrows to the basement.
동내 마을 (Dongnae "village") bus 10-1 stops in front of the Duck restaurant.
This place is one of the smaller gyms in town, but they make great use of their space, and it's got some great 100 move numbered problems to train on. They also show you where the key is so you can have the place to yourself if you climb in the morning. Other perks.. Free Chalk.