Calar Alto Observatory. This observatory, is located on the Calar Alto mountain in the Sierra Nevada, southern Spain. The domes are located at an altitude of 2168 metres. The site opened in 1975 and is operated jointly by the Max-Planck Institute for Astronomy and the Institute of Astrophysics of Andalusia. It is one of the largest observatories in mainland Europe, with several telescopes and domes.