The stated coordinates are not the location of the geocache. To find the cache, go to the coordinates, then follow the trail north around the reservoir to the end of the trail. There is a bridge at the end of the trail near a 낚시터 (fishing pond). The cache is not beyond the bridge.
If you have a compass, from the starting coordinates, the cache is 875 meters at 9°. Of course, you cannot walk straight there. You must follow the path to the last bridge on the trail.