The National Museum was a large museum in central London.
The Pandorica was displayed there in an alternate 1996, alongside stone Daleks and other things. Seven-year-old Amelia Pond and her aunt Sharon went to see it that year at Amelia's insistence, unaware that Pandorica contained her adult self.
Rory Williams, or rather the Auton duplicate of him, was employed as a night guard. He and the Eleventh Doctor rescued Amy's two incarnations from the stone Daleks. The Doctor subsequently launched himself in the Pandorica from within the museum in order to re-boot the universe. (TV: The Big Bang)