The historical industrial complex of Arnao is comprised of a coal mine and a zinc plant. The former was opened in 1833 by The Royal Asturian Mining Company (RCAM) and the latter was the result of the strategic diversification of the RCAM in the 1850s. Both are located in the maritime front line of the council of Castrillón, Asturias.
The RCAM coal mine was the first operational vertical shaft in Asturias, and is considered to be the first working submarine mineral excavation in Spain.
The coaling tower has been awarded the category of Monument a Bien de Interés Cultural (of cultural interest) and is the most singular example of the great valuable heritage that stands out in the industrial complex at Arnao.