Built under the command of D. João III in 1557 and completed in 1645 by D. João IV, who considered it the main key to the Kingdom through the sea, the Peniche fortress area has been used in several ways, according to the needs and historical changes of each period. Military square of vital strategic importance until 1897, shelter for Boer refugees from South Africa in the early 20^th century, dwelling for German and Austrian prisoners during World War I, political prison of the dictatorial Estado Novo (New State) from 1934 to 1974, temporary lodging of Portuguese families from the ancient ultramarine colonies in 1974 and, since 1984, housing the Museu Municipal (City Museum), the Peniche Fortress assumes special relevance as it is an important document of a local and national historical chronology.

The Peniche fortress is a National Monument since March 1938.