A dramatic opening on a wall that towers over the sea leads to the Grotta Zinzulusa, one of the largest karstic phenomena of Salento, just south of the town of Castro. The numerous concretions, (stalactites and stalagmites) found inside this cave reminded the local population of what they referred to as "zinzuli"  - old, threadbare clothes, hence its name.
Beyond the entry lies a karstic tunnel that penetrates inland for about one hundred metres, gradually narrowing until it reaches the Duomo, the final hall of the above ground stretch open to tourist. In fact, from this point on a drop in the level leads to the underwater part of the cave, the Cocito. Unique living fossils (hypegeum sponges Higghinsia ciccaresi)  were found here, as well as large stalagmites on the ground to witness a long period of emersion of these environments.