When I was in high school, I had the opportunity to visit the Cumberland Gap on the borders of Tennessee, North Carolina and Virginia. While up there, my family visited a cave there called Gap Cave. After walking in and following a path for a short while, it became very dark, with the only light coming from the National Park Ranger’s lamp. When we reached a large cavern, our guide stopped us and gathered everyone together. He then turned off the lamp, plunging us all into absolute, pitch-black darkness.