At the heart of the Parque Natural de la Sierra de Espadán, just outside Valencia, lie the San José caves, the site of the longest navigable underground river in Europe. Visitors are transported in a small boat, drifting along the mirror-calm waters of an underground lagoon, surrounded by stalactites and stalagmites that grow at the rate of an inch a century. The surreal landscape of the caves has given rise to picturesque names like the Dog Kennel and Diana’s Lake.
