Can I swim to the Benagil cave?

No, New local regulations don't allow boats to disembark passengers in the Benagil cave. Swimming to the cave from the Bneagil Beach can be dangerous due to the currents and tides. The only tours that allow you to get inside of the beach in the Benagil cave are the SUP tours (stand-up paddle) and kayak tours. These tours have a very high demand so we recommend to book on time ;) You can book using these pages:

SUP: https://www.seabookings.com/experience/sup-tour-in-benagil/

and

Kayak: https://www.seabookings.com/experience/boat-tour-kayak-tour-to-benagil/

Let us know if we can help any further. :)