This is a sweet gym! The park is very wel known by all taxi drivers and busses also run there. The gym isn't open on weekends, as it is a free to use Government amanity type gym. The walls are high - 12m I think and the left side has a few easier routes. The centre overhang section is wicked! Hard and intimidating,but lots of fun there too. The facilities are pretty damn good too. It's used for National comps at imes, so you'll find showers and bathrooms and some viewing platforms (great or telephoto zoom photography). The back section has some seriously steep cave bouldering, as well as some exercise equipment.
To get there isn't easy by car, unless you know the way. There are signs, but te roads are a bit confusing. Still, a search of Cheonan bus routes or a Cheonan street map should see you right. Just look or Taejosan Park.