10 Downing Street

That plain black door with the brass number 10 is one of the most recognized entrances on earth, yet it sits on what was once a fairly ordinary row of townhouses built by a man named Sir George Downing in the late 17th century. Downing was a diplomat and property developer, and the street quietly bearing his name would eventually become the center of British political power.

The transformation began in 1732, when King George II offered the house to Robert Walpole, who is widely considered Britain's first Prime Minister. Walpole accepted on one condition: that the house belong to the office, not to him personally. That single decision is why every Prime Minister since has lived and worked here. He then hired the architect William Kent to merge three separate townhouses into one residence of around 100 rooms.

The iconic black door itself came slightly later, designed in 1766 by architect Kenton Couse. For centuries the street was open to the public, but security gates were installed in the 1980s to protect its residents from modern threats.

So the next time someone tells you they have an important address, you can remind them that history's most powerful postbox belongs to a street named after a property developer.