The very first mention of the Gassan Shrine dates back to the 10th century. It worships the god of the moon: Tsukiyomi no Mikoto ツキヨミノミコト. On top of being the god of the moon, Tsukiyomi had to take on the responsibility for food, crops, and fishery after he killed the goddess of food: Ukemochi no kami. Hence, the Gassan shrine is worshipped by both farmers and fishers.
The shrine opens its gates on July 1st for the Mitobiraki ceremony 御戸開き and closes on September 15th with the Mitojime ceremony 御戸閉め. (exceptionally, the shrine will cease its activities on August 31st in 2021.)