Travelling back to Holland with the boat from La Coruna ??

was just about to reply, but you beat me to it

There are 2 passenger ferries UK-Spain. Brittany Ferries http://www.brittany-ferries.co.uk/ run Plymouth-Santander, P&O http://www.poferries.com/ Portsmouth-Bilbao

There are occasional freight/container ships from Galician ports that run to the UK (and maybe also somewhere like Rotterdam) and have accommodation, but I think this is much reduced since the arrival of budget airlines - it is not a cheap option. Then again, it's cheaper than a cruise

Another option, very much a descendant of medieval practice, is to hire a sailing boat. I posted an item viewtopic.php?t=126 on a French outfit that would probably be willing. Best for a group, I would have thought, unless you're pretty wealthy.