Venture off to The Great Boiling Valley, Owakudani, via the Ashinoko Lake Cruise.
The smell of sulfur from the valley's volcanic activity will cause you to cover your nose at first, but be sure to brave the smell to taste their delicious kuro-tamago (black eggs).
But don't over-indulge, and be sure to limit yourself to only two and a half eggs. Each egg adds seven years to your life, but eating up to three is considered bad luck.
Find out more about Owakudani.