The 1,845-foot Alpine Tunnel cuts under Altman Pass and served the Denver, South Park and Pacific Railroad from Denver to St. Elmo and Gunnison. Completed in 1881 after 18 months of construction, it was the first train tunnel across the Continental Divide and was lined and supported by California redwoods. Unfortunately, those timbers are now so completely rotted that both ends of the tunnel have been sealed for safety, though minor damage in the tunnel had caused its abandonment in 1910. Limited traffic by that time had made the damage not worth repairing. The tunnel, however, continues to rank as the longest narrow gauge and highest railroad tunnel in North America.
The three-mile trail to the eastern end begins across the small bridge over Chalk Creek just beyond Hancock and climbs moderately. ATV's can make it part of the distance, but hiking is necessary to get all way to the remains of the station complex at the portal. The weather at this elevation of over 11,000 feet is subject to sudden changes, with windy cold experienced even during the summer months. The area is subject to snow from early fall to early summer.