In the eastern part of Kentucky, Cumberland Plateau is forested with mountains and hills, and has Kentucky's highest point of 4, 139 feet. In the Bluegrass Region, it's made up of meadows and rolling hills. All the way in the northwestern part of Kentucky is hilly land and is also bordered by the Ohio River. It is also called the Western Coal Fields. The Jackson Purchase has the lowest point of Kentucky and the swampy lowlands Mississippi flood plain. In the central part of Kentucky is the Mammoth Cave Region. The Mammoth Cave is the largest cave system in the world. The mapped and explored parts are 365 miles.