The Atacama Pathfinder Experiment (APEX) is a radio telescope located at 5,100 meters above sea level, at the Llano de Chajnantor Observatory in the Atacama desert, in northern Chile, 50 kilometers to the east of San Pedro de Atacama.
The APEX telescope is a modified ALMA (Atacama Large Millimeter Array) prototype antenna and is located at the site of the ALMA observatory. It is designed to find targets that ALMA can study in greater detail.