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

Human presence in the Sant Josep area is documented from the Upper Palaeolithic period, some 17,000 years ago, when human groups inhabiting the surrounding cavities took advantage 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 functioned as a water supply location, and the municipal authority even commissioned studies to improve the use of the flow both for consumption and for irrigation of the fields.

Declared a Historic-Artistic Monument in 2000, the Coves de Sant Josep constitute a karstic cavity formed over millennia by the action of water on limestone rock. The site has also been a space for traditional leisure for the local population, a function that coexists with its condition as a natural and heritage enclave of the first order in the province of Castellón.