MANJANGGUL LAVA TUBE.

Manjanggul (Korean: 만장굴) is a lava tube located in Gimnyeong-ri, Gujwaeup, Jeju City, South Korea. At up to 23 metres (75') wide, 30 metres (100') high and 8.928 km (5½ miles) long, it is the 12th-longest lava tube in the world and the second longest on Jeju Island, although a significant portion of the cave is closed to visitors. It is the only cave of the Geomunoreum Lava Tube System, considered one of the finest lava tube systems in the world, regularly open to the public. It is also part of the UNESCO World Heritage Site list, under the item Jeju Volcanic Island and Lava Tubes