Boca do Inferno
Time Out says
The most famous rocky formation in Cascais attracts plenty of sightseers that, every single day, will venture onto the boulders to peek at the sea and try to get the best possible photograph as a keepsake. Traipsing over the rocks until you get to the viewpoint makes for a very nice stroll; from there, you can admire the true power of the ocean, even in days when the tides are tame. Nearby is a Portuguese arts and crafts fair, open daily until 9pm.