This trail is a great adventure from the Trail of the Hiawatha near Taft, MT all the way down to St. Regis, MT. The trail ride is complete with a tunnel and several trestles and loads of viewpoints along the St. Regis River.
The trail parallels the river most of the way and even dives under I-90 a couple of times. There are a few places to access the trail by car all along the way so don't be too worried about the length being 32 miles. You can easily ride it in sections if needed.