The temple was built for Hathor - goddess of love, music, joy, and motherhood, often shown as a woman with a cow's ears or crowned with horns and a sun disc. People had worshipped on this spot for a very long time; there is evidence of a building here around 2250 BC, in the age of the Old Kingdom king Pepi I, and another in the Eighteenth Dynasty a thousand years later. But the great temple that survives is comparatively young by Egyptian standards. Its construction began around 54 BC, in the last years of the Ptolemaic dynasty, and the work of carving and decorating ran on into the Roman period under emperors like Tiberius and Trajan. On the rear outer wall, larger than life, are carved Cleopatra VII - the famous Cleopatra - and her son Caesarion, whose father was Julius Caesar.

Set into a ceiling in one of the temple's upper chapels was a circular star map known as the Dendera zodiac, carved in the first century BC. It is one of the most complete representations of the ancient sky ever found, mixing Egyptian constellations with figures we still recognize - the bull of Taurus, the scales of Libra. Napoleon's scholars sketched it. Then, in 1820 and 1821, a French antiquities dealer named Sebastien-Louis Saulnier hired an engineer, Claude Lelorrain, to take it. Using saws and gunpowder charges, Lelorrain cut the heavy slab out of the temple roof and shipped it down the Nile to France. It reached Paris and was eventually installed in the Louvre, where the original remains today. A plaster copy now fills the gap in the Dendera ceiling. It was Jean-Francois Champollion, the man who cracked hieroglyphs, who correctly dated the relief to the Ptolemaic age.

In the temple's crypts, narrow chambers carved beneath the floor, is a relief that has launched a thousand internet theories. It shows a snake emerging from a lotus flower, the whole scene enclosed in a large oval that looks - to a modern eye primed by science fiction - uncannily like a light bulb. A fringe of writers have seized on it as proof that the ancient Egyptians had electricity. The reading does not survive contact with the actual evidence. The accompanying hieroglyphs explain the scene plainly: it depicts the god Harsomtus, a form of Horus, being born as a serpent from the lotus of creation. The oval is a hen vessel, associated with the womb of the sky goddess Nut. Egyptologists note the obvious problem with the light-bulb theory too - in a civilization this well documented, not one wire, socket, or shard of a bulb has ever been found.

What makes Dendera unforgettable is that you can walk almost all of it. Few ancient Egyptian temples are this accessible, from the subterranean crypts to the roof itself. A processional staircase climbs to the top, its steps so worn and overgrown with mineral accretion that visitors have nicknamed them the melted stairs - the literal erosion of thousands of priests' feet over millennia, rendered in stone. On the roof, chapels once hosted the festival of the New Year, when Hathor's statue was carried up to be touched by the rays of the rising sun. The Supreme Council of Antiquities has been restoring the complex in phases since 2005, cleaning the great pillared hall and reviving its painted scenes. The work goes on. Slowly, Dendera is being returned to the way its builders meant it to be seen - blazing with color, under a painted sky.