South of Souel, the Spongepack Trail starts from the South Gate (Nam Moon). There is an obvious uphill trail next to the outside part of the fortress wall. Take it and continue until it goes back down a little and hits another paved road. This road wont have traffic, as its a military road that actually takes you away from the fortress and to the next mountain to the south. At the top is a military base, about 2 km away. Just shy of the bases parking lot, there is a little dirt area on the left side of the road, with a gravel road going uphill to a little lookout some 50 meters away, some kind of tank parking space or something, and Spongepack going downhill. Heading on this trail, you ll be going up and down for 10 - 20 minutes, and there will be many turn-offs. Just stay on the dominant trail and dont make any sharp turns off of it. Eventually youll end up on a rough dirt road. Turn right and go downhill for a minute or two. Right before an imposing climb, look left. There should be a hidden little gem of a mountain bike singletrack going down. Take it all the way down to the bottom, through a farm and follow your nose to a two-lane road that connects Songnam and Hannam. Hannam is downhill but far, and Songnam is uphill and far. If you go towards Hannam, turn left onto a highway, heading north, and continue for about 30 minutes to Namhan Sansongs western entrance I described above. From the South Gate to the end of the singletrack is about 5 km.
Info courtesy of Steve Danyo
Overall, Spongepack Trail is the 2nd most popular mountain bike trail of all 7 mountain biking rides in Korea.