Jusanji was dug in 1721 as an irrigation reservoir for the farms below — it is about 200m long, 100m wide and 8m deep, and in three hundred years it has never run dry. What makes it extraordinary is the roughly thirty willows growing directly out of the water, some of them two or three centuries old, their trunks submerged and their crowns above the surface.
It is at its best in the ten minutes after sunrise in late October, when mist sits on the water and the reflections hold. Korean film-goers know it from Kim Ki-duk's <em>Spring, Summer, Fall, Winter… and Spring</em>, which was shot here.
The mountain proper takes its name from a legend: a Chinese prince called Juwang is said to have hidden in these gorges after a failed rebellion. Daejeonsa, the temple at the entrance, is traditionally dated to 672 and attributed to the monk Uisang.
The whole area is volcanic — welded tuff, eroded into the spires and slot gorges that make the valley walk so unusual — and it now sits inside the Cheongsong UNESCO Global Geopark.