West of Sun Valley, the Placer/Castle Creek route is an eleven mile mountain biking route climbing 1500.
To reach the mountain biking trailhead from Ketchum, head west on Warm Springs Road (FS227) for 15 miles. Park at the near Placer Creek (about 5 miles beyond Frenchmans Bend Hot Springs).
The route starts by heading northwest up the dirt road along Placer Creek for 2 miles. After the road turns to trail, veer right on poorly marked trail. After several more miles of climbing, begin a descent down to Castle Creek. Turn right heading southeast along Castle Creek leading back to Warm Springs Road.
Overall, Placer/Castle Creek Trail is the 27th most popular mountain bike trail of all 63 mountain biking rides in Idaho.