Puente del Inca is a natural stone bridge that has been coloured by a mineral spring. The bridge spans the Las Cuevas River in the high Andes, and the water, rich in sulphur and iron, has stained the rock in streaks of orange, yellow and rust. Hot springs rise beneath it, and the surface is coated with mineral crusts that look like paint. It sits at about 2,700 metres, in a valley of scree and bare mountains, with the white mass of Aconcagua, the highest peak in the Americas, somewhere beyond the ridges to the south.
Despite the name, the bridge was not built by the Inca. It formed naturally, as ice, sediment and mineral-rich water bonded together over thousands of years. The Inca did use trails in the region, but the colonial and later periods saw far more traffic, with mule caravans and travellers crossing on their way between Argentina and Chile. In the early twentieth century a hotel and thermal baths were built beside the bridge, and the ruins of that complex remain, a ghostly cluster of buildings half swallowed by the mineral deposits. Because of safety concerns, access to the bridge itself is limited, but you can see it from nearby viewpoints.
The road, Ruta 7, climbs to the site in broad bends along the valley, with a good surface and mountains closing in. The air is thin and cold, and the wind can be sharp. A line of small stalls sells souvenirs, mineral rocks and snacks, and a few simple cafes offer hot drinks and empanadas. The scenery is stark, and the colour of the rocks, red and ochre in the sun, is striking.
Uspallata, to the east, is the last reliable place to refuel on the Argentine side, and you should fill up before you start the climb, because the distances and altitudes ahead use more petrol than you might expect. The road beyond Puente del Inca leads to the Cristo Redentor tunnel and the old pass, and conditions depend heavily on the weather. In winter, snow and avalanche risk can close the road, sometimes for days.
Altitude can affect you, so take it easy and drink water. A short walk around the viewpoint is enough, and the late afternoon light makes the rocks glow.