Niihama is a city located in the eastern part of Ehime Prefecture, Japan. As of 31 July 2022, the city had an estimated population of 115,824 in 57781 households and a population density of 490 persons per km². The total area of the city is 234.50 square kilometres (90.54 sq mi). It has the third largest population in Ehime, behind the prefectural capital of Matsuyama and the recently expanded city of Imabari. It is famous for its Besshi copper mine as well as the annual Niihama Taiko Festival that is the center of annual drunken and boisterous activity and draws tourists from around the country.

The Seto Inland Sea , sometimes shortened to the Inland Sea, is the body of water separating Honshu, Shikoku, and Kyushu, three of the four main islands of Japan. It serves as a waterway connecting the Pacific Ocean to the Sea of Japan. It connects to Osaka Bay and provides a sea transport link to industrial centers in the Kansai region, including Osaka and Kobe. Before the construction of the San'yō Main Line, it was the main transportation link between Kansai and Kyūshū.