Serras de Aire e Candeeiros Natural Park (PNSAC) is a natural park in central west Portugal. It occupies an area of and is the most important repository of limestone formations in Portugal with a variety of geological formations associated with karst topography such as caves (including pit caves), sinkholes, uvalas, poljes, limestone pavements, ponors, among others. It was made a protected area in 1979 with the intend to protect the existing natural aspects and the architectonic and cultural heritage linked to the local populations.
The park is located in the central-west region of Portugal defining the border between the districts of Leiria and Santarém. It comprises part of the municipalities of Alcanena, Alcobaça, Batalha, Leiria, Ourém, Porto de Mós, Rio Maior, Santarém and Torres Novas.
PNSAC is mainly composed by mountain ranges (Serras) and plateaus: The Serra de Aire () in the northeast; the Serra de Candeeiros () in the west, adjacent to Aire, between Porto de Mós and Rio Maior; the Santo António plateau in the centre and part of the São Mamede plateau in the north.
The park is located in the Estremadura Limestone Massif, a geomorphological unit of Portugal where rocks from the Jurassic flourish to a great extent. The massif was created by the distensive opening phases of the Lusitanian Basin during the Mesozoic and the alpine compressive regimes established from the end of the Cretaceous. The São Mamede Plateau and Serra de Aire are the result of a rollover anticline.
With a vigorous and rugged landscape, the park has some of the most interesting geological formations in the country.
The nature park is evidenced both by its relief, as a prominent mass that rises about relative to its surroundings, and by its white, highly permeable limestones, which are dissolved by the relatively abundant rains, creating cracks where water infiltrates. These characteristics justify the absence of shallow watercourses, and the presence, instead, of a vast network of underground galleries, being perhaps one of the largest freshwater reservoirs in the country, giving rise to some important water courses, such as the Alviela and Lena rivers.