Akiyoshido Cave sounds like one of those places that makes you realize just how much cool stuff Japan has hiding underground. We're not talking about some little cavern here - this is Japan's biggest limestone cave system, stretching for NINE kilometers!

The setup seems perfect too - they've got the regular tourist-friendly route with paved paths (because Japan never makes you scramble through caves in the dark), but they've also got this "adventure path" for anyone feeling a bit more Indiana Jones. Inside, you've got the full cave greatest hits: limestone pools, underground waterfalls, and this cobalt blue stream running through it all.

Unfortunately, we couldn't make this happen. But I wanted to include it so it's on your radar.