The gothic styled Palácio Nacional de Sintra is situated in the heart of Sintra and was the most lived in royal residence, being continual used from the 15th century up until the fall of the monarchy in 1910. This is the palace that king Afonso VI (1650s) was imprisoned during his later life, as he was deemed, by his brother, too unstable to rule the country. http://www.sintra-portugal.com/guides/sintra-things-to-see.html