Drivers enter Las Raices one direction at a time, headlights swallowed by 4.5 kilometres of rock, and emerge on the far side of the Andes. There is room for only one lane, so a toll station upstream meters the traffic and waits for the bore to clear. For most of the twentieth century, this narrow tunnel through the mountains was the longest road tunnel in all of South America, a record it held for decades, and it remains one of the great quiet feats of Chilean engineering.
The tunnel pierces the southern Andes about 700 kilometres south of Santiago, carrying Route 181-CH from the city of Temuco toward the Pino Hachado pass and the Argentine border beyond. Trace that road on a map and its ambition becomes clear. It forms part of a continental link from the Pacific coast at Lebu in Chile all the way to Bahia Blanca on the Atlantic shore of Argentina, an artery stitching two oceans together across the width of South America. At 1,010 metres above sea level, Las Raices is the high, dark keyhole through which that whole crossing must pass.
The idea took decades to become a hole in the rock. Feasibility studies began in 1911, the final blueprints were ready in 1929, and construction started in 1930. Crews worked from both ends, one camp set in the Sierra Nevada and another at Boca Norte, boring toward each other through the heart of the range. The work lasted roughly eight years and consumed more than 32 million Chilean pesos of the day before the road tunnel was inaugurated in 1939. The finished bore runs 4,528 metres long, just 4.2 metres wide and 5.6 metres high, dimensions that explain why, to this day, only one line of traffic can pass at a time.
The tunnel led a second life on rails. From 1956 the railway between Pua and Lonquimay ran straight through the same mountain bore, and for nearly four decades trains rattled along this section until the line fell silent in the 1990s. The history of a place like this is easy to overlook from the road; it reads as just a long dark passage. But threaded through that darkness is a whole century of effort, of feasibility studies and blueprints and rail timetables, all aimed at the single stubborn problem of getting through the Andes rather than over them.
For the people of Lonquimay, the town on the far side, the tunnel is not a curiosity but a lifeline. Their valley sits in the high Andes where winters are ferocious, the temperature plunging toward minus 25 degrees and snow piling deep enough to close the mountain passes for months. When the surface road over the Cuesta de Las Raices vanishes under drifts, the tunnel stays open, holding the only reliable thread between the valley and the rest of the Araucania. This is country of the Pehuenche, the people of the pewen, whose communities still gather and sell the araucaria pine nuts that have sustained them for centuries. The dark bore through the rock is, for them, the difference between connection and a long winter cut off.
For those unwilling to surrender the view to a tunnel, the old way still exists. The Cuesta de Las Raices, a scenic gravel road, climbs over the mountains instead of through them, branching off about 5 kilometres before the western portal or 11 before the eastern. It is slower and rougher, the route that the tunnel was built to replace, but it trades efficiency for the sweep of high Andean country that the bore hides from sight. Down on the highway, some 450 vehicles a day still take the dark option, among them the heavy fuel trucks grinding in from Argentina, headlights vanishing one direction at a time into the mountain.
Las Raices Tunnel lies at 38.52 degrees south, 71.52 degrees west, beneath the southern Andes of Chile's La Araucania Region, carrying Route 181-CH at about 1,010 meters above sea level toward the Pino Hachado pass and Argentina. From the air, the tunnel itself is invisible, but its line is marked by the highway threading between major volcanic landmarks: Lonquimay (2,865 m) rises just to the north and Llaima (3,125 m) to the south, with Conguillio National Park nearby. A viewing altitude of 8,000 to 10,000 feet shows the mountain pass and the road's approach through forested foothills. The nearest major airport is La Araucania International (ICAO: SCQP) near Temuco, roughly 100 km west. High-country weather is changeable, with snow common in winter (June to August) closing the higher routes; clearest conditions come in the austral summer.