Seven Wonders of the World
The Seven Wonders of the World was a term applied to a number of man-made structures from Earth's history. The Eleventh Doctor listed it when going through things "important" about the number seven when the Shakri cubes started their countdown with that number. (TV: The Power of Three)
An attempt was made by Pholonius Ginn to collect them all and sell off them to the highest bidder on G-Bay. The wonders were: the Great Pyramids of Cheops, the Temple of Diana at Ephesus, the Colossus of Rhodes, the Statue of Zeus at Olympia, the Mausoleum at Halicarnassus, the Pharos Lighthouse at Alexandria and the Hanging Gardens of Babylon. (COMIC: Minus Seven Wonders)