Puente del Inca, Natural arch in Las Heras Department, Argentina.

Puente del Inca is a natural arch of travertine and cemented debris over the Las Cuevas River, 53.4 m long, 27.6 m wide and 10.2 m thick, rising 19.2 m above the water. Its rounded, asymmetrical mass is tinted green, orange, yellow and ochre by microbial communities and thermal water; stalactites hang beneath it. A grey stone building with an arched entrance and two square windows stands on the left bank above the deposits.

Cementation of debris flows from megaslides off the south wall of Aconcagua began roughly 14,798–13,886 years ago; the arch opened about 8,620–8,254 years ago through the retreating erosion of the Cuevas River. Charles Darwin visited in March 1835 and drew the bridge with its large stalactites. In the early 20th century a hotel, church and thermal baths were built, abandoned after a 1965 avalanche; the site became an intangible zone in 1991.

The name Puente del Inca links the natural arch to the Inca road network, the Qhapaqñan, which crossed this Andean pass and is now a UNESCO World Heritage Site. The abandoned early-20th-century bath pavilion beside the arch held separate pools fed by different thermal springs, and a tunnel connected it to the hotel.

The site sits directly along Route 7 between Mendoza and the Chilean border, with parking areas and easy access from the roadside. The best period to visit is between November and March when snow conditions in the mountains are more favorable and the road is safer to travel.

The water still seeping through the formation maintains a temperature around 33 degrees Celsius and constantly changes the surface color patterns. People used to bathe in the natural pools, but access is now closed to protect the geological structure.