LOUISVILLE, Ky. (AP) -- A cave system in Kentucky that's known as the longest in the world has reached 400 miles.
The National Park Service says Mammoth Cave in south central Kentucky recently added 10 miles to its explored underground length. The popular attraction for cave enthusiasts attracts volunteers who spend thousands of hours each year scouring the cave's winding caverns. The park service made the announcement over the weekend.
Charles Fox, president of the Cave Research Foundation, says the new length was measured thanks to many incremental additions in many parts of the cave, instead of one big discovery. The foundation is made up of volunteer explorers.
The cave attracts about 700,000 visitors a year and last year it opened a new $16 million visitors center.