Ryusendo Cave, Iwaizumi

Ryusendo Cave is one of Japan's three great limestone caves, located in Iwaizumi Town in Iwate Prefecture. Designated as a Natural Monument by the Japanese government in 1934, the cave system has been explored since surveys began in the 1920s. The total confirmed length of the cave is currently 3,631 meters, though the full extent may reach 5000 meters into the mountainside. The cave has a depth of 249 meters from the entrance to its lowest point, making it the 5th deepest in Japan. The cave opened to the public in 1967.

The cave's primary attraction is its system of underground lakes fed by crystal-clear spring water. Eight underground lakes exist within the cave system, with three lakes accessible to visitors, measuring 35, 38 and 98 meters deep respectively. The water displays a distinctive blue hue known as "dragon blue," illuminated by special underwater lights suspended deep into the lakes. A fourth lake, 120 meters deep, remains closed to the public and holds the distinction of being the deepest recorded underground lake in Japan. The cave's water is renowned for its purity and serves as the water supply for the town of Iwaizumi.

Visitors explore nearly 700 meters of accessible cave passages via elevated walkways, bridges and stairs. The route follows an underground river through spacious caverns and vaulted galleries, with viewing platforms offering perspectives from above. The cave maintains a constant temperature year-round, staying around 10°C regardless of season. The path includes several flights of stairs to a chamber just 35 meters below the mountain surface. Five species of bats inhabit the cave, including greater horseshoe bat, eastern long-fingered bat, brown long-eared bat and Hilgendorf's tube-nosed bat, which visitors may observe hanging from ceilings. These bat colonies are also protected as part of the natural monument designation.

The cave is located two kilometers outside of Iwaizumi Town center. Public transportation requires taking a bus from either Morioka or Miyako. Four direct buses by JR Tohoku Bus operate daily between Morioka Station and Ryusendo Cave, taking approximately 135 minutes and costing 2710 yen one way. This route is fully covered by the Japan Rail Pass and JR East Tohoku Area Pass. Alternatively, four non-JR buses per day operate between Ryusendo Cave and Iwaizumiomoto Station (25 minutes, 620 yen), from where Sanriku Railway trains run to Miyako City (35 minutes, 780 yen). These buses and trains are not covered by JR passes.

Admission costs ¥1,000 for adults and ¥500 for students, with the ticket providing access to both the main cave and the science museum. The typical visit takes approximately one hour to explore both sites. Visitors should bring warm clothing as cave temperatures remain cool even in summer, and rain gear is advisable as water drips from cave ceilings. The route includes staircases, some exceeding 200 steps.