Cave of El Castillo, Puente Viesgo, Cantabria.
It has only one entry. It has been modified -enlarged- in order to make researchs in a right way.
At the original design, building access was done through a little door. A natural ramp, today endowed with a staircase, led to the first room.
From this room, an access passing two galleries with litttle rooms finished at the main nave. The latter one is big and has an impressive stalagmitic whole.