A megalithic temple raised between 3600 and 3200 BC on a cliff facing the islet of Filfla, a thousand years before Stonehenge. The coralline limestone blocks are enormous — one weighs twenty tonnes — and a slot in one apse is aligned so that at the summer solstice the sun casts a disc of light across the floor. A canopy now shelters the stones; the sister temple of Mnajdra is ten minutes downhill.