What is in fact a single cave with three different entrances extends beneath the village of Valporquero de Torío. Formed between 23 and 5 million years ago, water continues to bore out the cavity. Neutral lighting accentuates the varied concretions and colours - 35 shades of red, grey and black (due to the presence of iron oxide and sulphur) have been identified here. Because of the temperature (7°C) and the slippery floor, visitors are advised to wear warm clothing and suitable footwear.