Indian Tunnel is a large lava tube named for mysterious stone circles near its path. Ancient stone structures appear in many places throughout the Monument, and archeologists believe some may have had ceremonial significance, though their precise function is unknown. The Shoshone used lava caves for shelter and as a source of water during their travels through the lava lands. Sunlight entering through openings in the roof allows travel through the cave without a flashlight. Measuring 30 feet high, 50 feet wide, and 800 feet long, the tube is large enough to allow comfortable walking through most of its length, and those willing to scramble over a large rock pile and climb through a small opening can exit at the far end.