Travel context
The gateway shapes the journey.
Douro planning normally begins from Porto and then narrows into rail, road, boat, tour, and overnight-base choices. Ericeira normally begins from Lisbon and tests whether the traveler can keep the stay centered in town. Benagil normally begins with an Algarve base and a separate access decision.
Those are very different travel patterns. A short trip becomes weaker when it combines them simply because each pin looks attractive.
No-car is a final-mile question.
Public transport can solve a gateway without solving the last transfer, dispersed beaches, vineyard visits, trailheads, luggage, or the return after a timed activity.
Treat no-car planning as a chain of decisions rather than a yes-or-no label. Check exact timetables and current services with the official transport operator.
A fallback day is part of the route.
Atlantic and Algarve coast plans depend on conditions. The Douro also changes with heat, road conditions, transport disruption, and booked visits. A credible itinerary needs a useful day even when the original activity cannot run.
That principle is especially important at Benagil, where current maritime rules and notices override evergreen travel copy.