The St. Paul Pass Tunnel was a railway tunnel in the northwest United States at St. Paul Pass, on the Montana-Idaho border. The tunnel was on the main line of the Chicago, Milwaukee, St. Paul & Pacific Railroad, commonly known as "The Milwaukee Road." With ongoing financial problems which worsened in the 1970s, the Milwaukee line abandoned its right-of-way in the West in 1980, but the tunnel and its approach grades have been revived as a rail trail route for hikers and bicyclists, the Route of the Hiawatha Trail.