The Kazumura lava tube system, within the 500 year-old ‘Ailā‘au lava flow of Kīlauea, is more than 40 miles (65 km) long and is thought to be the longest lava tube cave in the world. Tubes may be up to several dozen feet wide.
40 miles 40 miles (65 km) long
40 miles 40 miles (65 km) long