The Three Sisters are an unusual rock formation in the Blue Mountains of New South Wales, Australia, on the north escarpment of the Jamison Valley. They are located close to the town of Katoomba and are one of the Blue Mountains' best known sites, towering above the Jamison Valley. Their names are Meehni (922 m), Wimlah (918 m), and Gunnedoo (906 m). The formation receives more than 600,000 visitors per year. The Three Sisters were formed by land erosion around 200 million years ago during the Triassic period when the sandstone of the Blue Mountains was eroded over time by wind, rain and rivers, causing the cliffs surrounding the Jamison Valley to be slowly broken up. (Source: Wikipedia.org, CC BY-SA)