Mammoth Cave National Park in Kentucky was already a major tourist attraction when a team discovered that the Mammoth Cave System was connected to the nearby Flint Ridge Cave System, which was at the time the longest cave system ever explored.
Spelunkers from the Cave Research Foundation had sought the connection throughout the 1960s, and they finally made it when a six-person team emerged from Hanson’s Lost River into Mammoth Cave’s Echo River (interestingly, Hanson’s Lost River was named for 1930s explorer Pete Hanson, who had already come most of this way before he was killed during World War II).
Now, the limestone cave includes more than 400 miles of mapped labyrinth, with additional offshoots discovered every year. This makes the Mammoth-Flint Ridge Cave System more than twice as long as the world’s next-longest known cave system, in Mexico.
At the national park, tourists squeeze into the damp darkness by the hundreds for ranger-led tours of artificially lit areas such as Grand Avenue, Frozen Niagara and Fat Man's Misery. More adventurous types can take tours lit only by the lamps they carry. “Wild” tours take hard-core cave lovers into tight, muddy spaces with no clear walkways, giving them a feel for what the area's first explorers encountered.