The tunnel and the bridge of Cerro Salomón: some formidable ruins of the Riotinto Railroad. https://www.outono.net/elentir/2023/05/31/the-tunnel-and-the-bridge-of-cerro-salomon-some-formidable-ruins-of-the-riotinto-railroad/ They were part of the railway line of the Riotinto mining basin, in Huelva, Spain. Aventuras Entresierras showed them in one of their videos.