Wedged into the square's northwest corner, this building was constructed in 1772 as the headquarters of the Spanish vice-governor. After several reincarnations as a post office, the palace of the Senate, the Supreme Court, the National Academy of Arts and Letters, and the seat of the Cuban Geographical Society, the building is today a well-stocked bookstore.

Pop-art fans should take a look at the palace's Sala Galería Raúl Martínez. The building was being renovated at the time of writing.