Sea bathing was already becoming popular in Portugal in the mid-1850s. Cascais, with its protected beaches, was attracting tourists from the capital, Lisbon, and the numbers increased considerably following the opening of a road to the capital in 1863 and the commencement of a stagecoach service. Further stimulus for people to visit Cascais came as a result of the first visit to the town by Queen Maria Pia in September 1867 and the completion of a road from Sintra to Cascais in 1868. Sintra, situated in hills and therefore cooler in the summer, was a popular summer retreat for the Royal Family and the nobility of Lisbon.
Following renovation of the house of the Governor of the Cascais Citadel, the Royal Family stayed there for several weeks in 1870 and did so in subsequent years. It rapidly became normal for the nobility to leave Sintra and transfer to Cascais in early to mid-September in order to be close to the King. However, the quality of hotels in the town was considered poor and noble families began to construct their own homes, beginning with the Duke of Palmela and the Duke of Loulé. In time, rich businessmen also built summer houses, including Jorge O'Neil, a tobacco baron, and Henrique de Sommer who became Portugal's leading cement producer.
In design the new houses were rather different from the houses owned by the nobility in Lisbon, and came to be referred to as summer architecture. They were eclectic, both in their individual designs and in the wide range of architectural styles chosen by the owners, and aimed for a high level of external decoration. Architects used included Thomas Henry Wyatt from England and the Portuguese Raul Lino, who designed around 700 projects in his lifetime and developed the idealized concept of A Casa Portuguesa or the Portuguese House. Styles used included Italianate, Swiss chalet style, English Gothic, Louis XIII style, and neoclassical. The Palácio do Conde de Castro Guimarães used a Revivalist approach that included Neo-romanticism, Neo-Gothic, Neo-Manueline and Neo-Moorish styles.
Following the overthrow of the monarchy in 1910, there was not the same imperative for affluent citizens of Lisbon to be in Cascais every September. Nevertheless, the building of exotic summer houses continued and extended to neighbouring Estoril, which was becoming a popular resort area and opened a casino in 1916. 
Examples of summer architecture
- Palácio do Conde de Castro Guimarães
- Casa Sommer
- Palmela Palace
- Casa de Santa Maria
- Casa Verdades de Faria
- Henriques, Joao Miguel (2016). Cascais: 650 Years. Cascais: Cascais Municipality. pp. 53–61. ISBN 9789726372752.
- Briz, Maria da Graça Gonzalez. "A arquitectura de veraneio : os Estoris 1880-1930". Repositorio Universidade Nova. Retrieved 24 September 2018.
- Baptista, Maria Isabel Andrade. "Casas com história e memória em Cascais: um itinerário turístico pedestre". Repositório Comum ESHTE - Escola Superior de Hotelaria e Turismo do Estoril. Retrieved 25 September 2018.
- "Summer architecture route" (PDF). Cascais Municipality. Retrieved 24 September 2018.
- Ramalho, Maria. "Casa dos Almadas". Patrimonio Cultural. Retrieved 24 September 2018.
- "Palácio do Conde de Castro Guimarães / Torre de São Sebastião". Sistema de Informação para o Património Arquitetónico. Retrieved 20 January 2018.