Known by the Maltese as "L-Ahrax Tal-Mellieha" which means "hard rock". The entrance, very narrow, is from the sea if not by swimming or kayaking.
From the web:
Note: The populating of the files of the Heritage database proceeds in incremental phases: cataloging, georeferencing, insertion of information and images. The cultural property in question has been cataloged, georeferenced and the first information entered. In order to enrich the information content, further contributions are welcome, if you wish you can contribute through our area "Your Contributions"
Find out more on Database of the Material Heritage of Sicily and Malta
Get to know the Sicilian Cultural Heritage databases: Data Maps Heritage