According to Wikipedia, the Parthenon marbles in Britain has been repeatedly asked (by the Greek government, then by UNESCO itself) to be returned to its original Athens, Greece location. They were literally taken out of Greece by an Earl of England claiming (with no paperwork!) authority from the empire occupying Greece at the time.

There is a literal museum in Greece containing every part that wasn't stolen this way, in their exact original placement, waiting for the stolen pieces to be returned to complete it. And the British are still resistant.