There are regular ferry services between Portsmouth and Plymouth,England and  Santander/Bilbao, Spain :

There are also cruises which arrive at or start from Vigo and La Coruña with a range of companies promoting tours and excursions including:

There are also a very popular ferry service from Vigo to Cangas or the Cies Islands and Baiona to the Cies Islands in summer. In addition, the car ferry from northern Portugal to La Guardia is open all year which makes for an adventure when entering Galicia from Portugal.