There is a limit to the level of adaptation; mountaineers refer to the altitudes above 8,000 metres (26,000 ft) as the "death zone", where it is generally believed that no human body can acclimatize.
Climbing Chachani is popular, and many tour agencies in Arequipa offer guided trips to the summit, though the altitude is considered highly challenging for those who are not fully acclimatized.
The Illinizas are excellent mountains for acclimatization to altitude, and are frequently used as a preparatory climb to higher peaks such as Cotopaxi, Chimborazo and Cayambe.