The Blue Grotto is seven sea caves under a free-standing limestone arch thirty metres high, on the south coast of Malta. They open off one small inlet, Wied iż-Żurrieq, and everything here happens in the same water. An open wooden boat takes you and eight or ten others out of the slipway, under the arch and into the caves behind it. The skipper cuts the engine inside and the sound drops to water knocking on stone, with blue light sliding over the ceiling above you. The blue is not in the water itself. The floor is pale limestone and the water above it is clear, so the sunlight that reaches the bottom comes straight back up into the vaults. It only works with the sun high, so the boats go in the morning, and they only sail on a calm sea.
The same inlet is where the island swims. Through the summer Maltese families take over the flat rocks by the slipway and go in off the ladders into deep water with cliffs on both sides — the same clear water that lights the caves. A pull-off on the road above puts you outside the arch rather than under it, so the whole span reads with boats passing beneath for scale. The flat islet of Filfla lies low on the horizon behind it. On days when the sea is too rough to sail, that is your whole visit. The caves were not cut by the sea alone, either. Rain percolating through the limestone dissolved the first hollows while the Mediterranean stood lower than it does now, and the waves came later, forced into those weaknesses and brought down roof sections until the arch took its shape. Divers walk in from the same slipway the children jump off. A few hundred metres out lies the Um El Faroud, a 110-metre oil tanker scuttled here in 1998, its deck, funnel and engine room open between fifteen and thirty-six metres. A winter storm broke it in two where it lay.