The Cascais Citadel Palace Museum is situated inside the grounds of the Citadel of Cascais, in Cascais, Lisbon district, Portugal. Formerly the residence of the governor of the citadel, it was refurbished for use as the summer residence of the royal family, which spent September there annually from 1870 until the assassination of Carlos I in 1908. It was subsequently used as one of the official residences of Portuguese presidents, but over time fell into neglect. After extensive restoration it was opened as a museum in 2011. The palace forms part of the Museum of the Presidency of the Republic,, which has its headquarters at the Belém Palace in Lisbon.