The Summer Palace lies in the northwest of Beijing, about 10 kilometers away from the center of the city. It covers an area of 290 hectares, about three-fourths of the total area is water, and one-fourth is land and hill. The Qianlong Emperor of the Qing Dynasty (1644-1911), who commissioned work on the imperial gardens on the hill in 1749, gave Longevity Hill its present-day name in 1752, in celebration of his mother's 60th birthday. The Summer Palace is a vast ensemble of lakes, gardens and palaces in Beijing, China. The Summer Palace is mainly dominated by Longevity Hill and the Kunming Lake. Longevity Hill is about 60 metres (200 feet) high and has many buildings positioned in sequence. The front hill is rich with splendid halls and pavilions, while the back hill, in sharp contrast, is quiet with natural beauty. The central Kunming Lake covering 2.2 square kilometres (540 acres) was entirely man-made and the excavated soil was used to build Longevity Hill. In the Summer Palace, one finds a variety of palaces, gardens, and other classical-style architectural structures. In December 1998, UNESCO included the Summer Palace on its World Heritage List. It declared the Summer Palace "a masterpiece of Chinese landscape garden design. The natural landscape of hills and open water is combined with artificial features such as pavilions, halls, palaces, temples and bridges to form a harmonious ensemble of outstanding aesthetic value." It is a popular tourist destination but also serves as a recreational park.