It makes a great afternoon out from Porto to catch the old, bone-rattling No 1 tram from just below S Francisco church to the Foz terminus. From there it’s about 1km walk through the Passeo Alegre gardens running alongside the Douro estuary towards the sea. New vistas open out back towards Porto as far as the first bridge and over to Gaia and its beaches on the other side. As you pass Sao Joao castle, the Foz beaches appear. Head for the Lighthouse pier, rather than the one terminating in the red and white river mouth marker. You’ll you find (amateur) fishermen and huge views all directions along the coasts and back towards the city.
Beware though: even on a quiet sunny day, it’s very bracing. Don’t even attempt it in bad weather, the waves break right over the pier head.
You can’t get inside the lighthouse itself, & there is not much else except the views, but you’ll get a sense of achievement on having reached it.