The Cave of Los Marranos is located in Venta de Fresnedo, within the municipality of Lamasón, Cantabria. To access it you have to follow a path that leads directly to be upwelling of two mouths. Geologically it is something like a drain in times of floods, although it has a large lobby with rock art.

It was discovered in the 50s of the twentieth century, and in it are remains of the Paleolithic represented mainly by lithic carved in quartzite. On the other hand, there is a bronze buckle from the late Middle Ages, which indicates the possibility that the cave could have served as a shelter for travelers.