I'm no geologist but this cave must be a faultline in the rock. It is basically a straight tunnel that runs for many kilometres underground. The cave floor is wet year round (and is home to eels). After squeezing through the narrow entrance the tunnel runs for several hundred metres before the first 'siphon', which comes up to above your neck in water with the cave roof a few centiemetres above the water. Apparently a second siphon follows further on that requires the use of diving equipment to get through, and beyond this are many kilometres more of tunnel.
This is a really a tunnel rather than a cave. The entrance is door sized and pitch black but as you feel your way in you start to see light from the other end where it opens up onto the vertical cliff face, about 70m above the sea. The Cavalleria lighthouse is quite impressive anyway and the tunnel adds a bit of extra interest.
This cave is so well hidden you almost don't know it is there until you are in it. The entrance is just wide enough to get a boat in and once inside the chamber has a high roof. There are several ledges which are good fun for diving from and the water is plenty deep enough.
This is a great cave for anyone not really into caves. It is always a nice walk trying to find it - with nice smells of vegetation in the gorges as you walk up or down the paths - and it is dry, spacious and really quite pleasant inside. The shade can also be very welcome in the summer.
Without wishing to spoil it too much the cave has a fairly small entrance leading to a large cavern. It is quite spectacular and well worth a visit.