Blue Grotto, Malta

Where it sits. The Blue Grotto is not a single cave but a run of sea caverns in the cliffs of Malta's southern coast, immediately west of the tiny harbour of Wied iż-Żurrieq. In Maltese it is Taħt il-Ħnejja — beneath the arch — after the great natural span of rock that stands clear of the cliff at the entrance to the main cavern and forms the outline every photograph of the place is built around. Although the boats leave from Wied iż-Żurrieq, which belongs to the town of Żurrieq, the caves themselves fall inside the boundary of Qrendi, a distinction settled by a legal dispute between the two councils in 1910 and still cheerfully disputed in both villages. The cliffs here run up to about seventy metres and are pierced along their base by wave-cut hollows.

Why the water glows. The colour is a straightforward optical effect and no less striking for it. Sunlight entering the water outside the cave is scattered and filtered, the red end of the spectrum absorbed within the first few metres, and the surviving blue light bounces off the pale sand and rock on the seabed and up onto the cavern walls and roof. Because the caves face roughly south and southwest, the effect is strongest in the morning, from about nine until the early afternoon, when the sun is at the right angle to drive light under the arch. Different caverns give different results: some produce the luminous electric blue the site is named for, others a deep, almost violet dark, and in a few the encrusting sponges and algae throw back reds, oranges and greens.

The boats. Trips leave from the slipway at Wied iż-Żurrieq in small open wooden boats holding eight to ten passengers, run by a cooperative of local operators. The circuit takes about twenty to twenty-five minutes and visits several of the caverns in turn, including the main grotto, before returning. Boats do not sail in strong southerly or southwesterly winds, and swell can shut the operation down for days at a time in winter; a phone call before travelling saves a wasted journey. There is no advance booking system worth speaking of — tickets are bought at the quay on the day, and the queue is at its shortest before ten in the morning and after three in the afternoon, which unfortunately does not coincide with the best light.

The view from above. Half a kilometre back along the road from Żurrieq there is a walled belvedere on a bend where the whole composition lines up: the arch, the cliff line running east, and the flat-topped islet of Filfla five kilometres out to sea. This is where nearly every published photograph of the Blue Grotto is taken, and it costs nothing. Late afternoon light works better here than in the caves themselves. Filfla, visible from the same spot, was used as a naval and air force bombing range until 1971 and is now a strictly protected reserve holding one of the Mediterranean's larger colonies of European storm petrel, along with an endemic subspecies of wall lizard; landing is prohibited.

In and around the inlet. Wied iż-Żurrieq itself is a narrow slot in the cliffs with a concrete quay, a handful of kiosks and cafés, and boathouses cut into the rock. Above it stands Sciuta Tower, completed in 1638 as one of the small coastal watchtowers built under Grand Master Lascaris and restored by the heritage organisation Din l-Art Ħelwa. The inlet is a well-known dive site: the walls drop steeply, there are swim-through caves and a reef running out towards Filfla, and visibility here is among the best on the island. Swimming is possible from the rocks at the mouth of the inlet, though the surge deserves respect. A short distance east, the deep gorge of Wied Babu comes down towards the sea and offers a rough walking route with a view straight along the cliffs.

Getting there and timing. Buses run from Valletta in around fifty minutes and from Żurrieq village in ten; there is a car park above the inlet that fills by mid-morning in summer. The descent from the road to the quay is by steps and a steep ramp. April to June and September to October give calm mornings, warm water and manageable queues. July and August are hot and heavily coached; winter is beautiful and often unsailable. Bring cash for the boat, and expect to get wet in the bow.