Petimata ot 'Mobi Dik' (1970)

Two boys, two girls - all at that charmingly ambivalent age between childhood and maturity, and a little Vasko start out for a small island on board a sailing boat. Only the cactus hunting of the "old salt" Pedro disturbs the silence of the island. In an underwater cave near the island, the boys discover a group of saboteurs who have sunk their boat. While the boys engage the intruders in a real battle, Pedro swims to the mainland and brings along the coast guards. The ending could not be happier, and one is left wondering whether it all really happened.