Regularly voted one of Britain's most beautiful beaches, Barafundle Bay is a scenic 10-minute walk south along the coast path from Stackpole Quay (turn right). It is a gorgeous spot but its reputation has put paid to seclusion, so on summer weekends it can get pretty crowded despite the lack of road access. Come out of high season and you may just have the whole place to yourself, though.
If you're up for more walking, follow the coast path south of the beach out onto Stackpole Head with its impressive cliffs and rock arches.