Hi, having just visited Sintra, I would highly recommend you hire a private guide, we used Wonder Vans and were so happy we did. Tomas lives in the area and knew the streets and how to navigate and could just drop us off at the entrance the sites. I would be very stressed if I was driving as the streets are very narrow and many are one way. Apparently there are up to 25,000 people/day during the summer. Tomas has a special pass which allows you to purchase skip the line tickets on the day you visit, which is great. Make sure you visit Quinta da Regeleira it’s a magical place. Hope you enjoy your Sintra trip.