I would have to agree with what I think is a consensus here - unless you have a compelling reason to go by train/ferry (such as particularly enjoying that mode of transport, or a particular hatred of air travel), then fly - it's cheaper and far, far quicker.

If you're in no hurry, however, there are plenty interesting places you could stop off en route - North Wales, Chester, London, Brussels/Amsterdam, Cologne (and more if you take a less direct route).