Ryuga Cave — Limestone Cathedral Underground

Ryuga Cave (龍河洞) is one of Japan's three great limestone caves, a 4-kilometer underground system carved over 175 million years by the Yamadarui River as it dissolved its way through the Shikoku limestone karst. The public walking route covers 1km and takes you through chambers filled with stalactites, stalagmites, flowstone curtains, and underground pools lit by colored spotlights. The highlight is the 'Crystal Palace' chamber, where calcite formations hang like frozen chandeliers.

The cave is also an archaeological site — Yayoi-period pottery (2,000+ years old) was discovered deep inside, calcified into the cave floor by dripping limestone, creating eerie half-stone, half-ceramic artifacts. Ryuga Cave is less polished and more adventurous than famous caves like Akiyoshido — lighting is minimal in places, paths are narrow, and the sense of being deep underground is visceral.