Schwefelhöhle Zakynthos is a boat-reached cave-and-grotto dive on southern Zakynthos with sponge-covered rock, a dark overhead chamber, and a sulfur layer that can turn part of the route milky. It suits careful divers who want a guided route and steady Mediterranean fish life, and it is easiest when you move slowly through the entrances, keep buoyancy tight, and let a local guide handle timing around the cave openings.