The tiny town of Sintra and its vicinity are packed with historical buildings and attractions recognized by UNESCO as valuable examples of architecture and culture. The key place to visit is a castle built on the hills of the Serra da Sintra—the mountain that gave the name to the town. After some climbing, you can wander in the Castle of the Moors and to enjoy a view from Sintra as the mountain is high enough to play the role of an excellent viewing platform.
The colorful Pena Palace, National and Monserrate Palaces, and plenty of other historical buildings meet you at each corner of Sintra. Together with green and serene parks and forests, they turn the town into a perfect spot for spending a day or two away from Lisbon.
As Sintra belongs to the Sintra-Cascais Natural Park, you may take a short ride to rest on the vast beaches of Cascais, to explore Cabo da Roca—the westernmost point of the mainland Europe, or to take a walk in coastal villages. Even though it is a rather touristy area, it's indeed an unforgettable experience to stand on the edge of the continent.
The best time to visit Sintra, explore its castles and hike around is outside of the summer months namely from October through May. During this time the town is not as crowded, and the weather is not too hot. Winter months might bring rain showers, but the temperature is about 10-15°C so it's still quite pleasant to walk around. And the queues promise to be shorter.