Blue Mountains National Park covers about 664,000 acres of wilderness, and is one of the UNESCO World Heritage Sites. It is considered one of the popular destinations for many tourists and hikers, as it includes walking and cycling paths, many rivers, waterfalls, valleys, and others. It also has the Katoomba railway, which is the most dangerous of its kind in the world; The park is so named because of the blue mist emanating from the many eucalyptus trees that live in it.