I have visited this unique WHS several times. It is my favourite WHS in Malta and it is also considered to be the only underground neolithic temple in the world. It has only been discovered early in the 20th century and it is pretty much intact. Several archaeological remains have been placed in the National Museum of Archaeology to help preserve them better. The highlight of this site for me is the incredible acoustic effect that can be achieved in the main chamber, 3 storeys underground. A must-see in Malta but you have to book ahead online to be able to visit.