The Coves de Sant Josep are home to Europe’s longest navigable underground river, with a total length of 2,750 metres, 800 metres of which form the tourist route. They are located in the municipality of Vall d'Uixó, at the entrance to the Sierra de Espadán Natural Park. The tour is undertaken by boat, passing through galleries and lakes where the water has shaped the rocks over thousands of years. They also represent the longest cave system in the province of Castellón and the second longest in the entire Valencian Community.

Human presence in the Sant Josep area has been documented since the Upper Palaeolithic period, some 17,000 years ago, when groups of people living in the surrounding caves made use of the fresh water from the underground river. The archaeological sites found in the area confirm this continuous occupation, and there is evidence that the caves were already known in Iberian times. The site has historically served as a water supply point, and the local council even commissioned studies to improve the use of the water flow for both consumption and irrigation of the fields.

Declared a Historic-Artistic Monument in 2000, the Coves de Sant Josep are a karstic cave system formed over millennia by the action of water on limestone. The site has also been a traditional leisure spot for the local population, a role that coexists with its status as a natural and heritage site of the highest order in the province of Castellón.