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Postcard showing the entrance to the Red Cave in Royat-les-Bains, Auvergne, with a sign indicating 'RED CAVE ENTRANCE' and a stone staircase. The printed text states that the cave contains a curious source of carbonic acid. On the reverse, handwritten correspondence addressed to Monsieur Serrur in Boulouze, with a 5-centime green stamp and a cancellation.