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,[1] although a significant portion of the cave is closed to visitors.

[2] It is the only cave of the Geomunoreum Lava Tube System, considered one of the finest lava tube systems in the world,[3] regularly open to the public.

[4] It is also part of the UNESCO World Heritage Site list, under the item Jeju Volcanic Island and Lava Tubes.

Between entrances 1 and 2, there is a lower level main tube where most of creatures living in the cave can be found.