Sanmu is a city located in Chiba Prefecture, Japan. As of 1 November 2020, the city had an estimated population of 50,321 in 22,397 households and a population density of 340 inhabitants per square kilometre (880/sq mi). The total area of the city is 146.38 square kilometres (56.52 sq mi).

Kujūkuri Beach is a sandy beach that occupies much of the northeast coast of the Bōsō Peninsula in Chiba Prefecture, Japan. The beach is approximately 60 kilometres (37 mi) long, making it the second longest beach in Japan. Kujūkuri Beach is a popular swimming and surfing destination for inhabitants of Greater Tokyo. The beach is protected as part of Kujūkuri Prefectural Natural Park.