Praia da Marinha is the archetypal Algarve cove. Clear turquoise waters lap up against the orange limestone that forms the cliffs and iconic rock formations that have graced the covers of a hundred holiday brochures. The beach itself is fairly small and sandy, but what has saved it is what it doesn't have. Despite being located in the middle of the Algarve coast, Praia da Marinha lacks the facilities and most importantly, the easy access of other Algarve beaches. To get to the beach involves a bit off a drive off the main road followed by a steep descent down to the beach via a set of steps.
If you can convince the whole family to negotiate the steps down to the beach then it is a kids wonderland of nooks, crannies and caves to explore. The snorkelling is great and relatively safe although there isn't any lifeguard cover. Boat trips (including paddle boat hire) are available from the beach so you can explore the weird and wonderful rock formations at close hand.
Marinha beach can be found by turning off the main EN125 between Portimão and Carvoeiro by the Algarve International School. From here it is about 4km to the beach.