S P O T ／ SPOT-303

Ryusendo Cave

龍泉洞りゅうせんどう

Deep in the mountains of Iwate, one of Japan's three great limestone caves hides a color you have to see lit to believe. Ryusendo runs an estimated 5,000-plus meters into the rock, of which about 700 are open to visitors, and its signature feature is a chain of underground lakes fed by water so clear it barely registers as water at all. The Third Underground Lake plunges 98 meters straight down, and where the lights hit it the pool sinks into a deep, glowing indigo the cave's keepers call "Dragon Blue" — a saturated, otherworldly blue that looks less like a flooded cavern and more like a window opened onto somewhere it should not be possible to see. You walk it on railed catwalks that hug the rock and tilt out over the drop, peering down into water whose floor is plainly visible meters below the surface. Designated a National Natural Monument together with the bats that live inside it, and rebuilt after catastrophic flooding in 2016, Ryusendo remains one of the eeriest and most beautiful natural sites in all of Tohoku.