Sintra is reached quite easily by car from Lisbon. Leaving town on the A37 motorway to the west you will get to the A16, from where you can follow the signs to Sintra (travel time from the airport approx. 25 minutes). Be aware that Sintra itself is dreadful for car traffic, also because of the large number of tourist buses coming into town. Most roads are one-way only, and side streets are extremely narrow and often steep. The best is to park your car in one of the free car parks at the outskirts of town, and walk from there. (Sintra Wikitravel)