Aucanquilcha is a massive stratovolcano at an elevation of 6,176m (20,262ft) above the sea level, located in Antofagasta Region of northern Chile. An old mine road used to run to the top, but now much of it above 5,500m has been wiped out by landslides. For several years, it was the highest driveable road in the world.
The biggest problem is the extremely low oxygen for engine combustion. This road is no longer usable by vehicles. The highest permanent human habitation was a miners' barracks at about 5,500 m (18,000 ft). Mining originally began on the volcano in 1913, initially using llamas as pack animals to carry down the sulfur. An aerial cable system extending for 22 km (14 mi) was completed in 1935, to lower the sulfur in buckets. Eventually this was replaced by the road which switchbacked up to the summit and was capable of supporting 20-ton mining trucks. Since the mine closed in 1993 much of the road has fallen into disrepair. It's one of the highest mountain roads of Chile.
Menacing desert terrain with numerous steep, rocky climbs. Large, sharp rocks require tight maneuvering, increasing the likelihood of tire damage. Sulphur mine workings at 6,000m on the north side of Aucanquilcha have been serviced by motor vehicles. The road was constructed all the way to the summit. Due to landslides, motorised use is no longer possible and cycles cannot be ridden along some stretches. At 5,334m, a nearby village of the same name is the world's highest permanent settlement. This is an extremely tough road to try and climb up on a bike. The terrible surface and steep gradients meant that with loaded bikes you will have to push about 80% of the way from 4,000m to a high point at 5,130m. Although a number of people have taken their bikes to the summit, the surface on many stretches of the road is very bad. However, there are sections of rideable road all the way to the summit. On the summit itself it would also be possible to ride around a bit.
Do not take this drive if you have respiratory problems or any type of heart condition. Notorius lack of oxygen that tests the organisms and a high degree of steepness. Most people feel altitude sickness at around 2,500-2,800 meters. Extremely low oxygen for engine combustion. The summit has about 40% less oxygen than at sea level, thus breathing is more difficult. The high elevation with its risk of altitude sickness, weather concerns, steep road grade, and overall inaccessibility make the pass dangerous and summit trips difficult. The existence of the old road makes it relatively easy to get to the summit on foot if you are well acclimatized and the old mining camp at 5,280m makes a good base camp as there are walls to shelter your tent. The winds in this area can be fierce and especially in winter the nights can be extremely cold. It’s one of the highest roads of South America.
Pic: Diego Delso [CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons