Koyagawa River runs through Shimonoseki City from north to south and flows into the Seto Inland Sea. Toyota-cho, Shimonoseki City, located in the upper reaches of the river, is the place where the firefly boat service started for the fist time in Japan. The fireflies that inhabit the Koyagawa River and its tributaries are designated as a national monument. The time when the fireflies start to fly and the number of fireflies differ slightly depending on the year, but the natural wild dance without calculation or prediction invites the viewers into a fantastic world. The firefly boats run about 800 meters, and local volunteers will be boatmen and guides. It's also fun to hear stories and deep knowledge unique to local volunteers.