Cerro Armazones, Mountain summit in Sierra Vicuña Mackenna, Chile

Cerro Armazones is a summit in the Sierra Vicuña Mackenna of Chile's Coast Range, about 105 km southeast of Antofagasta in the Antofagasta Region. Its summit was truncated during construction of the Extremely Large Telescope, leaving a plateau several metres below the former 3,064 m elevation. About 1 km southwest and 230 m lower stands the Polish Cerro Murphy Observatory.

On 26 April 2010 the European Southern Observatory Council chose Cerro Armazones as the site of the planned Extremely Large Telescope, whose main mirror is to measure 39.3 m across 798 hexagonal segments. Construction began in June 2014, and first light is scheduled for 2027. The summit was truncated to create the telescope platform.

The name Armazones is Spanish for "large frameworks" or "big crates", a mining-era reference rather than an indigenous term. The mountain's working life is scientific: the Polish Cerro Murphy Observatory, run by the Nicolaus Copernicus Astronomical Center in Warsaw, stands on a neighbouring hill about 1 km southwest and 230 m lower, and its observations are carried out by the Araucaria Project.

Cerro Armazones lies about 105 km southeast of Antofagasta and is reached by a service road built for the ELT project; the summit is an active construction site and not open to visitors. The site records roughly 350 cloudless nights a year, so daytime sun is intense and the air extremely dry. At over 3,000 m, altitude effects are felt quickly.

The mountain peak was deliberately reshaped by removing material to create a flat platform for the telescope facility. This topographical modification represents an unusual intervention that reflects the importance of the site for worldwide science.