The Blue Grotto (Maltese: Taht il-Hnejja) is actually a number of sea caverns on the southern coast of Malta, west of the Wied iz-Żurrieq harbor near the village of Żurrieq. It is located right across the small uninhabited islet of Filfla.
Every day from sunrise until about 1 pm a unique sight can be observed here. The location of the cave combined with the sunlight lead to the water mirroring showing numerous shades of blue. Several caverns mirror the brilliant phosphorescent colours of the underwater flora; other caverns show a deep dark shade of blue.
The Blue Grotto is a popular destination for tourists on the island of Malta. It was also used for a scene of the 2004 film Troy, starring Brad Pitt.