Vis Island, Dalmatia dive sites

During the Cold War, the Yugoslav People's Navy carved several underground military tunnels into the limestone cliffs of Vis Island to shelter submarines and fast patrol boats from aerial detection. The island served as a major military base and was closed to foreign visitors until 1989. After Croatian independence, the tunnels were abandoned and have since been colonised by marine life, creating a unique fusion of military history and underwater ecology.

An Open Water certification is technically sufficient as the tunnel maintains natural light throughout and the maximum depth is around 22 metres. However, Advanced Open Water or cavern diving experience is recommended because parts of the tunnel are enclosed overhead. All divers must be accompanied by a local guide who knows the structure and any hazards from deteriorating concrete and metal.

It is classified as a cavern dive rather than a true cave dive because natural light is visible throughout the tunnel from one or both entrances. The tunnel is wide and tall enough that a submarine could pass through, so there is ample space for divers. No cave diving certification is required, but comfort with overhead environments and good buoyancy control are essential to avoid stirring up silt from the tunnel floor.