Born from a volcanic eruption around 2,000 years ago, Japan’s mysterious Mashu-ko, or Lake Mashu, located on the island of Hokkaido, is rumoured to be one of the clearest lakes in the world.

Still, without hesitation, and a massive bag of Benadryl in my suitcase, I flew to Tokyo (Hanada Airport) to meet up with a group that would be traveling through East Hokkaido for a week. While we saw ...