The project is situated at the entrance of the Sado Estuary, a crucial location for the defense of Lisbon and Setubal. This place witnessed military occupations at various historical periods. Faced with abandonment and destruction, the intervention focuses on the site of the Old Fort (17th c.) and 7th Artillery Battery (WWII), located on top of a cliff. The proposal is defined by a new structure that connects the military buildings (Old Fort, Entrenched Buildings, and 3 Batteries) guiding visitors to understand and discover the place in a unique way. This new structure integrates a museum that features a permanent exhibition on coastal defense and temporary installations of contemporary art. The museum represents the overlapping of three distinct periods: the Old Fort period, the 7th Battery period; and the Museum period. Preserving, adapting, and rebuilding are interconnected actions, that form the very foundation of the museum project itself. The museum appears as a new mark in time connecting and adapting the pre-existing structures. The visitors’ journey is defined by a series of diverse spaces where light guides them through underground areas, creating a sense of surprise and wonder. The proposal works with the topography, mainly through underground spaces, employing the same camouflage logic used in bunkers. The project blends into the landscape, remaining invisible from the outside, without keeping the protagonist away from pre-existing heritage structures and preserving the protected landscape.