Kimberley's main tourist attraction is the Kimberley Mine Museum, an open-air museum centered on the "Big Hole".The Big Hole (the Kimberley Mine) is the world's largest man-made hole, with a depth of 800m/.5mi, a diameter of 470m/1,542ft and a circumference of 1.5km/.9mi. Between 1871 and 1914 22.6 million tons of earth and rock were excavated from the mine for a yield of 2,722kg/6,000lb of diamonds. Visitors can look down from a viewing platform into the mine, now filled with water to 150m/500ft below ground level.By 1889, when the workings had reached a depth of 400m/.25mi, opencast mining was no longer possible. Later the work was increasingly mechanized, the first winding tower being installed in 1892.