The Casa Sommer, inaugurated on 7 December 2016, houses the Municipal Historical Archive and the Municipal Library of Cascais.

This square-shaped house was built by Henrique Sommer in the late 19th century and is the most important and scholarly example of a neoclassical private residence in the town, as evidenced by the smooth, curved pediments and fluted pilasters, cartouches, mouldings and triglyphs on the exterior elevations. Its style is also marked by the main façade, preceded by a rectangular portico, resting on pillars at the corners, which frames the entrance and forms the noble balcony on the second floor, protected by a balustrade.

Casa Sommer underwent extensive renovation work, designed by architect Paula Santos, which also covered the old stables and included a new underground structure connecting the two buildings. This work allowed the Cascais Municipal Historical Archive to be reinstalled as a Local History Centre in a space equipped with the necessary conditions for the collection, organisation, preservation and dissemination of the precious documentation in its custody, which is fundamental for the reconstruction of the history of the municipality from 1387 to 2016, the extreme dates of the sources it makes available for consultation, currently organised into 100 Funds and Collections.