Tourist Souvenir Stamps

A set of stamps shwing the various caverns and features of Visitar la Gruta de los Maravillas or the Marvelous Grottoes of Aracena in Andelusia. Like many other limestone cave systems they were formed by dissolution of the rock by rain and ground water, and subsequent evaporation. They were opened to the public in 1914, and these stamps look as if they date not much after this. They have been used for scenes in Journey to the Centre of the Earth and Tarzan in King Solomon's Mines.
Last spring (2024) I visited some very similar caves at Nerja on the southern coast. These are probably formed within the same rock strata, but 100 km away.