The Elgin Marbles are on my list for my next visit, since I've now been to the Parthenon (which was undergoing some sort of structural restoration when I was there in 2008). At the time there was also a new museum being built near the Acropolis, I got the impression in part in order to make a case for the return of the Marbles by building a place where they could be kept. But things have kind of gone to shit in Greece since then (to oversimplify rather drastically) so IDK.