Chacaltaya: towards a solution of the knee...?

Cosmic rays physics is currently being studied with rather sophisticated detectors running in a variety of experimental conditions and atmospheric depths around the world. In this paper we describe the reasons why cosmic ray physics experiments at high altitudes like Chacaltaya are so important for resolving some of the open problems in cosmic physics. A discussion on the future prospects of the high-altitude mountain laboratories such as Chacaltaya for cosmic ray physics is presented.