Explorers have mapped out another 700 feet of Jewel Cave in the Black Hills to maintain its rank as the world's second longest cave.

Jewel Cave now has just over 145 miles of explored and mapped passageways.

The official length of a cave is not the distance between points, but rather the cumulative distance of all explored and mapped passages.

Mammoth Cave in Kentucky is considered the world's longest cave with 365 miles of explored passages.

Third on the list behind Jewel Cave is a cave in the Ukraine.