Nippara Limestone Caves

Very cool (literally) natural phenomenon

If you're after a unique place to explore in the Okutama area, I definitely recommend the Nippara Limestone Cave. It's apparently the largest cave in the Kanto area, and you can check out some neat formations when you're inside -- they also illuminate the cave with different colors, which I thought was fun. One thing to note is that it's cold inside the cave. It stays at around 10 degrees celsius which is fine if you're dressed for the conditions, but you may need to bring a jacket if you visit in summer, for instance.