Gunung Mulu National Park was inscribed as a UNESCO World Heritage Site in 2000. This picturesque natural wonder covers 52,865 hectares of primary rainforest that is dissected by several fast-flowing rivers and clear jungle streams. The oldest of Mulu's caves started to form about five million years ago. Heavy rain and continual erosion over the years have carved out the vast subterranean system that exists today. With its deeply-incised canyons, wild rivers, rainforest-covered mountains, spectacular limestone pinnacles, cave passages and features, Mulu has many outstanding scenic qualities.