A rails-to-trails project converted 15 miles of Chicago, Milwaukee, and St. Paul Railroad track, tunnel, and trestle into the exhilarating Hiawatha Mountain Bike Trail (208/744-1301, www.ridethehiawatha.com , late May–early Oct., trail pass $9 adult, $5 child). The centerpiece of the trail is the 8,771-foot Taft Tunnel, built in 1909 and cut through solid rock from the Montana side of Lookout Pass  through to Idaho. As the track descends into Idaho, it winds through another ten tunnels and over nine wooden trestles before reaching the valley floor.
Bikers need headlights to traverse the trail, and hikers will want to bring along strong flashlights. Be prepared to get a little wet and chilly in the tunnel. Even though the grade never exceeds 1.7 percent, vertigo-inducing trestles stand along sheer cliffs and over steep rocky canyons. Whether you’re on foot or on a bike, you’ll have your heart in your mouth on several occasions.
To reach the beginning of the trail and Taft Tunnel, take exit 5 (Taft Area) from I-90. Turn south and follow Rainy Creek Road for two miles, and take the road toward East Portal at the Y junction. The parking area is immediately ahead, and just beyond is the gate to the tunnel. The trail follows the contours of Loop Creek until it meets the Moon Pass Road, which leads to Wallace in 20 miles via Placer Creek Road. An additional 31 miles of trail, heading east to St. Regis, are in the works.
A shuttle service ferries cyclists back to Lookout Pass. Plan a full day for this trip, and reserve a spot on the shuttle in advance by calling the Lookout Pass Ski Area (208/744-1301, $9 adults, $6 children). Mountain bike rentals are available at the ski area (exit 0 from I-90) for $28–32; you can also rent a tagalong bike or a trailer for kids.