Sintra is indeed magic. The LP is right about not taking a car; parking is a nightmare even during weekdays. The best means of transport is the suburban train which is quite comfortable (A/C), fairly cheap and goes very frequently to and from Sintra.
While there they had just opened the Quinta de Regaleira to the public (briefly mentioned on P 131 of the LP Portugal guide). The house was bought by the city council at a very low price from Japanese developers who wanted to turn it into a hotel, but never got a license from the city elders to do so. Entrance fee is a bit steep at 2,000 Escudos (US$10), but it is well worth seeing. They have guided tours on the hour (except around lunch time) that last almost two hours. In my case, I was the only non-Portuguese but the guide was quite willing translate everything in English. She took us first through the garden where Carvalho, the then owner, basically recreated his vision of the garden of Eden. The garden and also the chapel inside the garden have some very interesting Freemason features. At the end of the tour, the guide also took us through some of the rooms of the house itself. Overall, a nice glimpse of how the like of late 19th century coffee tycoons lived like back then.