Manjanggul Cave

Manjanggul is a lava tube on Jeju Island, South Korea, part of the Geomunoreum lava tube system formed around 200,000 to 300,000 years ago by eruptions from the Geomunoreum volcanic cone. As fluid basaltic lava flowed downhill toward the sea, its outer surface cooled and solidified into a crust while molten lava continued flowing beneath, and when the eruption ended and the remaining lava drained away, it left behind a long hollow tunnel roughly 7.4 kilometers in length, one of the longest known lava tube systems in the world. Its interior preserves features distinctive of lava tube formation, including lava stalactites, flow lines on the walls marking successive lava levels, and a large lava column, and it forms part of the Jeju Volcanic Island and Lava Tubes UNESCO World Heritage Site.