The subway river Coves de Sant Josep, located in the place of the same name, is a natural cave located in the municipality of La Vall d'Uixó, province of Castellón, Spain.  The cave was developed in the Middle Triassic period and is composed mostly of limestone. The origin of the river and the end of the cave are unknown.  It is the longest cave in the province of Castellón, and the second longest in the Valencian Community. In addition, thanks to its water source, it is the longest navigable subway river in Europe.