The Cumbres & Toltec Scenic Railroad climbs 64 miles (103 km) of three-foot (914 mm) narrow gauge through the San Juan Mountains, linking Chama, New Mexico (7,863 ft / 2,397 m) with Antonito, Colorado (7,888 ft / 2,404 m). Between them the line crests 10,015-ft (3,053 m) Cumbres Pass — the highest point reached by any rail line in the United States — and crosses the Colorado–New Mexico border 11 times.

The railroad is the best-preserved surviving segment of the Denver & Rio Grande's once-vast narrow-gauge network (its sister line is the Durango & Silverton). Trains are pulled by coal- and oil-fired steam locomotives from the 1900–1925 era, including the heavy K-36 class 2-8-2 'Mikados', past original 1880s depots, water tanks and the Chama yard, which still functions much as it did a century ago.

Out of Chama the engines attack a sustained 4% grade — one of the steepest sustained mainline grades in North America — often double-headed for extra power. The route then threads two tunnels (Mud Tunnel and Rock Tunnel), edges the 600-ft-deep Toltec Gorge above the Rio de los Pinos, loops through Tanglefoot Curve and crosses the 137-ft-high Cascade Creek Trestle, the tallest on the line. All trains meet at the remote Osier Station (9,637 ft / 2,937 m) for a hot lunch at the midpoint.

For railfans the Cumbres & Toltec is a bucket-list pilgrimage: it is North America's longest and highest authentic steam railroad, and almost everything along its 64 miles — locomotives, rolling stock, depots, the Chama roundhouse and coal tipple — is original Denver & Rio Grande equipment, not reproduction. The line was designated a National Historic Landmark on October 16, 2012 and has been on the National Register of Historic Places since February 16, 1973.

It is also a feat of preservation politics: when the Rio Grande won approval to abandon the route in 1969, the states of Colorado and New Mexico jointly bought the 64-mile segment, nine steam locomotives and over 130 cars for $547,120 in 1970, then began hauling tourists in 1971. Today it is owned by both states and governed by the bi-state Cumbres & Toltec Scenic Railroad Commission, created by an act of Congress in 1974.

Riding the full line is an all-day affair of roughly seven hours, including the lunch stop at Osier. Because the 64 miles are too far to cover round-trip in a day, passengers ride one way by steam and return to their starting depot on a comfortable motorcoach — or split the trip over two days. Shorter options include the half-line 'Limited' trips that turn at Osier and the Express trips that sample the heights of Cumbres Pass in a few hours.

Every train carries an open-air gondola car free to all riders — the prime spot for 360-degree views, fresh mountain air and the sound of a working steam engine. Volunteer docents from the Friends of the Cumbres & Toltec narrate the geology and history. Classes of service run from Coach (padded bench seats, open windows) through Deluxe (café-style tables) to the 21-and-over Parlor and Parlor Observation cars, Victorian-style lounge cars with an attendant, morning pastry and afternoon snacks. Most tickets include the chef-prepared buffet lunch at Osier; a 7% Historic Preservation Fee is added to each ticket.

The line opened in 1880 as part of the Denver & Rio Grande Railroad's San Juan Extension, a 3-ft narrow-gauge route built to serve the silver-mining district of the San Juan Mountains in southwestern Colorado. After the 1893 repeal of the Sherman Silver Purchase Act, mining declined and the San Juan Extension never warranted conversion to standard gauge, leaving it frozen in 19th-century form.

In 1969 the Interstate Commerce Commission granted the Rio Grande permission to abandon its last narrow-gauge main line. Rather than lose it, Colorado and New Mexico jointly purchased the 64-mile Chama–Antonito segment, nine locomotives and more than 130 freight and work cars for $547,120 in 1970; tourist operations began the following year. The Cumbres & Toltec Scenic Railroad Commission, an interstate agency authorized by Congress in 1974, now sets policy, while the non-profit Cumbres & Toltec Operating LLC runs day-to-day service and the Friends of the C&TSRR (founded 1981) restore and interpret the historic fleet.

The defining engineering challenge is altitude and grade. From Chama the railroad pulls a sustained 4% grade for some 14 miles up to Cumbres Pass at 10,015 ft (3,053 m), frequently requiring double-headed or helper steam locomotives. Just below the summit the track doubles back on itself at Tanglefoot Curve, a loop tight enough that the locomotive nearly faces its own train.

Descending toward Antonito, the line crosses the Cascade Creek Trestle, a 137-ft-high (42 m) structure that is the tallest on the route, then bores through two tunnels — Mud Tunnel and Rock Tunnel — as it clings to a ledge roughly 600 ft (180 m) above the Rio de los Pinos in Toltec Gorge. Other notable structures include the high Lobato Trestle over Wolf Creek near Chama. The motive power is equally historic: surviving Rio Grande steam includes the K-27, K-36 and K-37 2-8-2 'Mikado' classes, with five locomotives in active service.

The railroad runs seasonally from late May through late October, operating Tuesday through Sunday. Summer (June–August) brings green alpine meadows, wildflowers and the fullest schedule, though afternoon mountain thunderstorms are common. Late September to mid-October is the signature window, when the aspen forests above Chama and along Cumbres Pass turn brilliant gold and the air is crisp and clear.

At these elevations — 7,800 ft at Chama up to 10,015 ft at the summit — weather changes quickly and mornings are cold even in summer, so dress in layers and bring sun protection for the open gondola car. Fall dates and the 21-and-over Parlor cars sell out earliest, so book well ahead for foliage season.

Seats are assigned at purchase and trains frequently sell out, so reserve in advance, especially for fall foliage and the premium cars; same-day tickets are sometimes available but not guaranteed. Wheelchair lifts are offered on select coach cars and the motorcoaches, but ADA accommodations must be arranged at least 7 days ahead, and wheelchairs cannot roll between the historic cars.

Spend time in the free open-air gondola for the best photography, but expect cinders and soot — a UV filter protects your lens. Restrooms are on the train, the motorcoaches, both depots and the Osier dining hall. Pets are not allowed (service animals only) and smoking, including e-cigarettes, is banned on all railroad property. Changes are accepted up to 24 hours before departure; refunds require 48 hours' notice.