Went on a weekend trip to Lisbon last December. The weather was perfect so I took the train to Sintra for a quick boulder sesh with one of the locals. We checked out Mecca and met this crew from super nice crew from California. We joined forces, stacked pads, and had one of the best outdoor sessions I've ever had.
Sintra is very cool but you definitely need a car to get around the different areas. I would suggest mecca for a first area. Lots of routes close together of all grades. There is a guidebook which is very good. I would reccomend the Boulder Sintra tour guides. They will make it worth your time if you dont have much to spare.