Mammoth Cave National Park preserves the longest known cave system on earth, with more than 400 miles of passages, as well as 53,000 acres of forest. It offers nearly a dozen miles of cave trail underground, nearly 70 miles of nature trail on the surface, 13 backcountry campsites, three campgrounds, and more than 20 miles of navigable river. In southern Kentucky, the area has a moderate climate with warm, moist conditions, summers in the high 80s, winters in the low 40s, about 50 inches of precipitation each year mostly in spring, occasional mild to moderate snow and ice in winter, year-round storms that can include tornadoes and flooding in low-lying areas, and a constant cave temperature of 54°F.