Ryusendo Cave — One of Japan's Three Great Caves with a Mystical Underground Lake

In the mountains of northern Iwate, beneath the forested ridges of the Kitakami Range, lies one of Japan's three great limestone caverns: Ryusendo Cave (Ryusendo-do). What makes Ryusendo unique among Japan's famous caves is the quality and color of its underground lakes. Fed by rainwater filtered through the limestone for decades before entering the cave, these still pools display a blue so pure and vivid — visibility reaching over 41 meters — that they seem to glow with their own inner light, a phenomenon that earned them recognition as some of Japan's clearest natural waters.

Highlights

The cave extends 3,600 meters into the mountain, though about 700 meters are open to visitors. The public section passes through dramatic chambers and narrow passages, progressively descending to three underground lakes. The third lake, at 98 meters depth, displays the most extraordinary blue — lit from the surface, the water appears almost luminous, ranging from pale turquoise to deep indigo depending on angle and lighting.

Limestone formations — stalactites, stalagmites, and flowstone curtains — decorate the cave walls, formed over hundreds of thousands of years. The cave maintains a year-round temperature of about 10°C, offering cool relief in summer and relative warmth in winter. Bat colonies inhabit deeper sections, and their activity influenced the cave's name ("ryu" means dragon, and local legend held that a dragon god lived within).

Getting There & Tips

The cave is in Iwaizumi town, accessible by bus from Iwaizumi Station on the Sanriku Railway. From Morioka, a direct bus service runs to Ryusendo on some days. Entry fee required. The cave floor can be slippery — wear appropriate footwear.

Best Time to Visit

Open year-round with consistent interior conditions. Summer is most popular but also most crowded. Weekday visits outside peak season offer the quietest experience. The cave's 10°C temperature makes it refreshing in summer and relatively warm in winter.