Exploring the amazing hidden environments that we have on Earth is helping us to contemplate and prepare for the Great Explorations to come beyond the planet of our birth. But it is not just exploration alone, but coupling that to science that results in the great discoveries and the expansion of the human understanding of the universe that we seek. We will take a tour of some of the most extreme cave environments on Earth and discuss their value to the furtherance of the search for life on other planets.