Centred on the river valleys in the southwest of the Northwest Territories, and accessible only by air, is the 1,840 square mile (4,766 sq km) Nahanni National Park, an outstanding example of northern wilderness with rivers, canyons, gorges and alpine tundra. One of the park's key features is the South Nahanni River, which originates as a small stream in the remote Mackenzie Mountains. In the park the silt-laden waters meander through scenic mountain valleys and hurtle through a series of deep canyons. Along the river are the Rabbitkettle Hotsprings, the Virginia Falls (with a vertical drop twice that of Niagara Falls), a series of river canyons and caves. Wildlife includes Dall sheep, mountain goats, woodland caribou, wolves, black bears, grizzly bears and trumpeter swans. Nahanni National Park was the first site in the world to be granted World Heritage status by Unesco in 1978. The very intrepid can reach the park via the badly maintained road (often impassable) to Tungsten, and then onwards by river, but most visitors fly in by chartered floatplane from nearby towns. Many operators offer day trips