Calatrava Volcanoes. Ciudad Real UNESCO Global Geopark is situated in the southwest of the autonomous community of Castilla-La Mancha, in central Spain. The “Volcanes de Calatrava” territory holds international geological significance, offering a chronological thread of distinctive volcanic episodes. The geopark houses the world's most prolific mining reservoir for mercury in the region of Almadén, which has been extracted for over 2,500 years. The strong presence of mercury is due to a submarine Surtseyan volcanic eruption, which occurred 420 million years ago, and you can find the only mercury mine in the world to have been exploited from Roman times to the present day.