An American cave explorer paddles across the beautiful Lake Castrovalva in Lechuguilla (cave), Carlsbad Caverns National Park, New Mexico. Before getting into the small inflatable boat, she had to change into clean clothes and shoes to be ready for entering this pristine area of cave. For millions of years, the cave has been sealed off from human and animal interaction. The cave is so beautiful and so important to science that access is strictly controlled in order to keep the cave in as pristine condition as possible. It is a real time machine, taking us back to a world that was very different to the one we live in today.