Shh, don't tell anyone else...
Up and down the coast there are many well-known beaches. But there are also plenty of lesser-known sandy expanses that attract little attention from the crowds. These beaches can be a haven even in the height of the season. In many of the more remote locations there are rough parking spaces where it is possible to camp. Watch the sunset or catch an empty morning wave. Many of these beaches are right next to much more popular spots. Seek and you shall find.
North of Ericeira near Ribamar lies Coxos. This break is certainly not a secret, but on its day is a world-class spectacle. The less experienced should come to watch but don't try to paddle out unless you are prepared to pay your respects to the locals or the rocks that this fierce wave breaks on.
Just over the hill from the hustle and bustle of Ribeira D'Illas lies its much less celebrated (but equally pleasant) brother, boasting excellent waves, especially towards low tide, and almost no crowds.
It has a van friendly car park and some facilities in the summer.