A great flat in a good location - highly recommended!
It is walkable to the center of Sintra, but be careful and take your time, as traffic can be dangerous. Be sure to park on R. Álvaro dos Reis (before you reach the apartment) because if you pass the apartment you'll quickly arrive downtown Sintra and getting back is very difficult after a certain point due to the tiny one-way streets.
Oh, and do yourself a favor and make a reservation at Tira Tapas right across the street.