Just over from the Azure Window is the Inland Sea:
Calling it a sea is a little bit of a stretch; it's really more of a puddle.
The hole in the cliff on the left is a channel to the sea. This is what lets the water flow in; it also allows small boats to go out.
It cost us 3.50 euros each, which is pretty good value compared to some of the other trips we saw.
Once through the tunnel, you're taken to see the Azure Window, and into some smaller caves along the cliff. Depending on the way the light catches the water, and what's at the sea bed, you can get considerable variation in the colour of the sea.
Above, you can see that it really is blue.
The boatmen also point out various features - what look like faces or animals in the cliff face. The following makes for quite a convincing crocodile: