Praia da Ribeira ("Ribeira beach") is Cascais' most centrally located beach, situated right in front of the village's town hall, Praça 5 de Outubro ("5th October Square") and the famous Baía hotel.
This emblematic beach is also informally known as Praia dos Pescadores ("Fishermen's beach"), because it preserves an entire infrastructure for small boats to unload all the fish and seafood on a daily basis.
It is very close to Cascais' historic center, the Citadel of Cascais and the Cascais Marina.
According to Google Maps, Praia da Ribeira isn't an official beach. In other words, it is not a bathing area from a legal standpoint. However, between March and October, on sunny days, it's practically impossible not to see anyone laying down at the sand strip, playing sports or going for a swim.
Make sure you also check Praia de Santa Marta ("Santa Marta beach"), which is just 1km (10 minutes by foot) away from Praia da Ribeira.