Sintra is usually visited on a day trip from Lisbon, but there’s way too much to see in a few hours. If you must—you can get there in 40 minutes on train from Lisbon’s Rossio station.
The major sites there are the Pena Palace (19th c.) and the castle Castelo dos Mouros (an 8th/9th century Moorish defensive structure, reconstructed in the 19th). There’s even a *Toy Museum*whose founder, João Arbués Moreira, believes one can “better understand the history of humankind through toys.” He has some 3000 year old Egyptian ones in the collection.
Where to stay in Sintra? The historic Lawrence’s Hotel is the oldest hotel in the Iberian Peninsula. Lord Byron slept there. You should, too.
Can’t make the festival? You should still visit Sintra. Easily done on a private tour from Lisbon