Can recommend Hendaia (Hendaye to the French) and Hondarribia (Fuenterabia to the Spanish), both on the estaury of the Bidasoa on the border between France and Spain.

A passenger ferry runs between the two sides of the estuary, from the Hendaia marina to the town of Hondarribia, about a 10-mins walk from the marina on that side.

If you are staying onboard for any length of time, you can "pick and mix" the two different atmospheres and cultures. The French side is quieter, the Spanish more populated and live. Served food is also better and mostly cheaper there too.

Both marinas are just a hop, step and jump from the local beach (plage to the French, hondartza to the Basques).

Sanitary facilities in both, when I last used them, were first class.