Washington Mini Monument - 2 15th St NW, Washington, DC, USA

Close to the real Washington Monument, there is a 12-foot-tall replica of the same monument, hidden under a manhole cover. The monument is officially called “Bench Mark A,” and is a Geodetic Control Point for the use of surveyors. It forms part of a network of control points across the USA which allows the National Geodetic Survey to synchronise all the government’s maps.