Pyramid of Khufu (Great Pyramid of Giza)

The tallest structure on earth for roughly 3,800 years. Its base is level to within about two centimetres and its sides are aligned to true north within a twentieth of a degree. The polished Tura limestone casing that once made it smooth and white was stripped for Cairo's medieval buildings; a little survives at the base, and more at the apex of Khafre's pyramid alongside.