text:  Mammoth Cave's system is just as massive as its name suggests. More than 400 miles of cave passage have been discovered thus far. The National Park Service says they're still discovering new ones. Welcome to Mammoth Cave National Park. My name is Ranger Quinton. You can't explore the cave in depth without a guide. And today, Ranger Quinton is leading a small group of guests, literally following in the footsteps of many before him. In the 1930s, an all-black Civilian Conservation Corps group