See this photo? This is what you can see if you go to a city like Sintra. Actually you can go there by bus ir train from Lisbon or everywhere in Spain. The thing is, if you have your own car or you rent a camper van, you will not have the freedom that a car gives you.
It´s actually an advice I´m giving you, because I was there 2 months ago and I saw the difficulty of walking and moving around all the city. The thing is, whenever you are there you will see you have to pay for bus or train a lot of money, so maybe it´s better if you hire a van.