The Hiawatha Trail is located in North Idaho right at the Montana state line. It used to be a railway. My family biked the 15 mile course in 2017 and then again in 2020.
You buy passes to ride the trail at Lookout Pass Ski Lodge, which is located right at the top of the pass between Idaho and Montana on I-90, the only freeway in the region.
There are tunnels that the trains used to travel through, blasted right through the rock. The longest one is more than a mile long and it's pitch black inside. You have to have strong headlights on your bike and a taillight. The ceilings drip and it's cold. Plus there are these deep ditches along each side for water drainage. So don't get too close to the wall.
The ride is easy because you start at the divide on top of the mountains and ride down a gentle slope all the way.
The views along the trail are drop dead gorgeous as well.
At the bottom you wait for a bus that carries you back up to the top of the trail and your vehicle . . . or you can bike back up.
Rating: 5 out of 5, would do again.