Before it gets there, it filters through porous lava rock, making it one of the clearest natural lakes in the world — in fact, the water is totally drinkable. Here's what it's like to scuba dive ...

For Lemonex, Inc., based in Seoul, South Korea, the inspiration came from a natural phenomenon: the porous lava rock found on the volcanic island of Jeju, 130km off the coast of the Korean Peninsula.