Manjanggul Cave is a lava tube under the eastern fields of Jeju island, in South Korea, more than seven kilometres long, one lit kilometre of which is walked to the tallest lava column ever recorded, a pillar of 7.6 metres joining floor to ceiling, in a tunnel that a village schoolteacher measured in 1946 with thirty of his pupils in straw shoes carrying pine torches. The tube was made when a river of lava from the Geomunoreum volcano crusted over and drained away, leaving a tunnel up to 23 metres wide and 30 high, with the marks of the lava's levels running along the walls as horizontal ledges at shoulder and head height, each the height the river held before it dropped; nobody agrees how old it is, with the dating of soils buried under the flows returning an age close to 8,000 years while other estimates run to 300,000, and the tube is part of the UNESCO listing of Jeju's volcanoes. The walk is flat and cool at 12 degrees on a wet floor, past Turtle Rock, a slab of hardened crust that drifted along on the moving lava and stranded here when the flow drained, in the shape of the island itself, to the column at the end, where the lava poured through a hole in the roof from a tube above and set in a pillar.
Beyond the barrier the tube goes on unlit to its third entrance, and the upper level near it holds the largest bat colony confirmed in Korea, long-fingered bats packed into the dark, with pups born in June and on the wing by late summer, the reason that section is kept shut, since the cave life there is richest. The tube lies under farmland twenty minutes from the coast and the lava flows of the same volcano run on to the sea at Woljeongri, and Seongsan Ilchulbong, the sunrise crater, is nearby. Manjanggul is a river of stone that emptied, and its last pillar is the tallest anyone has found.