The surrounding rocks forming the walls of the cave, do not quite reach the bottom of the ocean floor, and thus light seeps in, which creates the wonderful blue colour which surrounds you once inside.
Other than getting there by boat, there is also a pathway or bus from town which will take you to a landing just next to the entrance, from where the rowboat guys will pick you up.
To get into the grotto, you signal one of the rowboat operators who wait outside the entrance, and then transfer to their boat.
The entrance to the Grotto is a sight by itself, a small hole, through which people appear and disappear as the waves ebb and flow.
When in the boat, you actually need to lie down, so as not to crack your head, going through.
Our rowboat guy sang some opera, and explained the history of the site to us. We gave him a small tip (for which he'll ask), over and above the 8 euro we paid (per person) at the boat outside.

