10 Downing St

10 Downing Street has been the official residence and office of the British Prime Minister since the 1730s, its plain black door one of the most photographed doors in the world despite being seen only from a distance today, since a permanent security gate at the end of the street closed public access in the 1980s. Visitors can't approach the door itself, but the gated view down Downing Street from Whitehall is enough to draw steady interest, reflected in the data's high must-see score despite the brief, entirely free visit. It's best treated as a two-minute stop worked into a longer Whitehall walk toward Parliament Square rather than a destination on its own.