Beneath the sun-drenched hillsides of the province of Castellon, a river winds silently through a limestone labyrinth. The Coves de Sant Josep in the town of Vall d'Uixo offer one of Spain's most unusual cave experiences: a guided boat trip along nearly 800 metres of navigable underground waterway, the longest such stretch open to the public in all of Europe.
Geology and Formation
The cave system was carved over millions of years by the persistent action of water dissolving the Jurassic and Cretaceous limestone that underlies this part of the Valencia region. The subterranean river still flows today, feeding from rainwater that percolates through the hillside above before emerging into daylight at the cave mouth.
The explored portions of the system extend approximately 2,750 metres, though only a section is open to visitors. Throughout the navigable passage, the ceiling varies dramatically: in some places it soars to over 10 metres above the water, while at others it drops low enough that passengers instinctively duck, though the boats are carefully routed to ensure safe clearance.
The Boat Tour Experience
Visitors board flat-bottomed boats at the cave entrance, where the river flows out into a natural pool surrounded by Mediterranean vegetation. A guide rows the boat upstream into the cave, pointing out geological features and recounting the history of the site. The journey covers roughly 800 metres by water, followed by a short walking section through dry galleries decorated with stalactites and flowstone curtains.
The cave lighting has been carefully designed to highlight the most dramatic formations without disturbing the subterranean ecosystem. Along the route, visitors pass through several named chambers, including the Hall of Bats (Sala de los Murciegos) and the Blue Lake (Lago Azul), where the water takes on an intense turquoise colour under the lights due to its mineral content and clarity.
Human History in the Cave
Archaeological evidence shows that the caves have been used by humans for thousands of years. Fragments of Neolithic pottery and tools have been recovered from dry chambers deeper within the system, suggesting the cave served as a shelter or ritual site as far back as 15,000 years ago. During the Spanish Civil War, the outer chambers were reportedly used as a refuge by local civilians.
The caves were first opened to tourists in the 1920s, initially with candle-lit boat trips. Over the decades, access was improved, electric lighting installed, and the navigable route extended as speleological surveys revealed new passages. Today the site is managed by the local municipality and welcomes over 100,000 visitors annually.
Visitor Information
Exploring the Surroundings
Vall d'Uixo itself is a pleasant town with Moorish-era ruins and a lively weekly market. The region is part of the Valencia Community's "interior tourism" route, which connects rural villages, olive groves and citrus orchards. For those combining cave visits, the nearby city of Castellon de la Plana offers museums, a historic quarter and easy access to the Costa del Azahar beaches.
Nature enthusiasts may also enjoy the Sierra de Espadan natural park, located roughly 25 kilometres inland, which features cork oak forests, mountain trails and several smaller wild caves accessible with proper caving equipment and experience.