Kazumura Cave on the island of Hawaii near Kīlauea clocks in at 40.7 miles (65.5 kilometers) long and 3,614 feet (1,102 meters) deep. That makes it the longest and deepest lava tube in the United States and the world. Ape Cave in Skamania, Washington on the south side of Mount St. Helens stretches 2.5 miles long, making it the longest lava tube in the continental United States.