Kemmunett or Cominotto in English is a must see rock. It is located on the other side of Comino where the blue lagoon is. You can swim across or you can also go by boat there. I recommend you try and swim there early in the morning before all the tourists come. The water is just amazing how clear it is. Once you arrive at the Cominotto go into the cave and swim out if you are not afraid of dark blue colors.

But you have to be careful for two main thinks before you go. The weather needs to be good, so if there are waves, just don't go. be careful of jellyfish as well.