The one word I would use to describe Sintra is that it's quirky. Bizzare in the Alice in Wonderland kind of way. It's definitely a town overun by tourists, but I kind of like it in a its like this nightmare that has a pleasant feel to it.
How to get there & around:
There are several routes to reach Sintra by train from anywhere in Lisbon. If you have a Lisbon Zapping card, the card will pay from the train ride from Lisbon to Sintra.
Once you arrive to Sintra, I strongly suggest to purchase the bus ticket for the Sintra Loop Bus 434 to cover the main sights. This bus will take you to the Moorish Castle ruins and Pena Palace which are located on the hilltop and Quinta da Regaleira - the climb can get pretty steep so the bus is a godsend.
The Pena Palace reminds me of a fantasy story with its fairy-tale like motifs and bright wall colors. The Palace is located at the top of the hill and even after coming off the bus, there is a short climb before passing the castle gates.
Address: Address: Estrada da Pena, 2710-609 Sintra, Portugal
Quinta da Regaleira is another interesting site to visit in Sintra. The place is huge and you can take almost half a day exploring the estate.
The highlight of the estate would be the Initiation Well. You can walk down the well to the bottom which leads to some tunnels to other parts of the estate, which depending on the day, can feel a bit spooky exploring it.
Address: Quinta da Regaleira 2710-567 SintraPORTUGAL , http://www.regaleira.pt
Piriquita
If you have time to explore the town centre, take some time to visit Piriquita and try their famous Traveisseros and Queijadas.
Address: Rua das Padarias 1/18, 2719-603 Sintra , http://www.piriquita.pt/?lang=en