Tiny Doors in the U.S. Capitol (29122889536)

These small doors and the water sources they housed, found in several places in the Capitol Building, were multipurpose. They stood ready to provide water to prevent any future fire from spreading, but they also ensured the mud tracked in from Washington's dirt streets and footpaths could be easily cleaned from the Capitol's floors. That is why the doors stand only about 30 inches tall: they conceal low, shallow closets where workers filled pails of water to mop the floors.
Full story from Tholos at Meigs' Miniatures: The Story of the Tiny Doors in the U.S. Capitol.