In northern Japan, a two-mile ravine runs through the city of Ichinoseki. The powerful Iwai river cuts through ancient dacite tuff, laid down by the eruptions of Mount Kurikoma. This is Genbikei Gorge (literally, “severe beauty valley”). Millions of years of erosion has sculpted the stone into a variety of interesting shapes. It has been known as a scenic spot since the Edo period, and in 1877 even earned a visit from Emperor Meiji himself. One reason people love visiting the gorge is the opportunity to order “flying dango.” Dango…