The “Mini-Cruise” (way in which it is offered by the shipping company that links Plymouth with Santander) is a trip that lasts about 48 hours.
It leaves from Plymouth to Roscoff (French Brittany), with no possibility of disembarking, on its way to Santander, where passengers have three hours to get to know the city before getting back to the ferry; which will take them back to Plymouth after 20 more hours.