British Museum

Regardless of the protestations of the Greeks and others whose lands we have despoiled over the centuries, it is probably better for civilisation and posterity that the Elgin Marbles, amongst other antiquities, have been safely housed here than left to the vandalism, thievery and corruption of the locals. I have never really understood this obsession with returning things to their "rightful" owners after centuries have passed; just how far back would you go? In any case, why is it so terrible that the public can enjoy odd artworks in random places? At least, despite the moral blackmail at the entrance asking for donations, it is a fantastic museum and free (or at least already included in my taxes)...unlike similar institutions in other countries. So whether your special interest is Ancient Greece, Egyptian mummies, Roman sculpture, Benin Bronzes or something more esoteric (they even have moai from Easter Island), then there will be several decent examples to keep you happy.