Benagil Caves are very easy to paddleboard to from the beach. Although we took our own, there are plenty of places offering board rentals. You can also get to beaches that can only be accessed via the sea.
Just around the corner from Benagil is Praia do Carvalho. Access to the beach is via a tunnel.
A narrow staircase on the other side of the beach leads to some other tunnels.
We found a great free spot to camp overnight in between Benagil and Praia do Carvalho. Although we were quite freaked out in the morning when we found a strange man peering in through our open window!
There were some other amazing wild camping spaces there - worth a look if you're a fellow campervanner in the Algarve!