South of Souel, the Halftrack trail is a 27 km loop combining singletrack and paved. Start at the eastern entrance, go through the fortress wall to Halftrack (which begins right at the extreme east end of the wall (not close at all to East Gate (Tong Moon), and which may be difficult to find. The trail begins steeply from the top of a crumbling part of the wall itself! After a few minutes or 10, take a well-used singletrack on the left. Youll know you missed the turn-off if you arrive at a traditional grave instead. After 20 or 30 minutes (?) you ll come to a 50m or so walk-up. You can mountain bike ride down the other side (45 degrees!) or you can turn right before the walk-up and mountain bike ride down a fast little connector to a farm. Make a left on the country road and mountain bike ride for 5 minutes until you hit a highway. Turn right, and mountain bike ride slightly downhill for about 2 km (?) until you see the other paved entrance to the park on your right; this is the paved uphill I described above, about 8 km long. It will take you up to the East Gate (Tong Moon). Along the way, you can stop for food if you want.
Find your way to the West Gate (Seo Moon), which is actually in the northwest part of the fortress. Ride dramatically through the gate (the only way to mountain bike ride through that gate!), make a sharp right and mountain bike ride the trail that follows the outside of the wall. This part is very beautiful, and is a good place to rest. Ride for about 100 or 200 meters and look for a small modern watchtower on your left. When you spot it, youre facing north and Seoul lies in front of you in the distance. Take this trail to the watchtower, where there are more views. There are some steep, rocky sections here at the tower which may lead you to think the trails unmountain bike rideable. Just downclimb and mountain bike ride along the obvious ridge. Turn left on a well-used but easily unnoticed trail that descends for a few minutes to the western side of Hannam, which turned out to be perfect, since Olympic Park (in Seoul) was about a 15 minute mountain bike ride away, with the Han River Park just beyond. The best way to describe how to find the turn-off is this: after about 100 or 200 meters past the left turn, the trail starts going uphill and at the top becomes unmountain bike rideable again.
Info courtesy of Steve Danyo
Overall, Halftrack Trail is the 4th most popular mountain bike trail of all 7 mountain biking rides in Korea.