It is a fortress with a bastioned layout corresponding to the town's citadel and stronghold. The plan is irregularly polygonal, adapting to the rocky escarpment. It consists of two re-entrant structures (composed of two demi-bastions), a bastion and respective curtains, a small fort with a circular plan (the Round Fort, from 1557/58), and a ravelin that protects the only access gate. It is surrounded by a wet ditch on the landward side and by the rocky escarpment on the seaward side. The fortress is complemented by a bastioned urban front that defends the isthmus of Peniche, composed of a fort, four demi-bastions, a bastion, and curtains. The defensive system of Peniche is further articulated with the forts of Berlenga and Consolação and the Baleal fort. The structure was adapted as a prison facility starting in 1807. It is an important symbol of contemporary Portuguese history for having served as a political prison during the Estado Novo regime. Currently, it houses the National Museum of Resistance and Liberty. It includes the Chapel of Santa Bárbara. Its transformation into a political prison and subsequent conversion into the National Museum of Resistance and Liberty give the fortress an extremely strong symbolic significance, transcending its purely military or architectural value. Its preservation is, as such, intrinsically linked to the recent political memory of Portugal.