Ypur routes aren't displaying for me, for some reason.

Europe is big and extremely diverse. You could agonise for months about your route and still be forced to miss lots of places that are well worth seeing, and riding through.

Were I starting from Shannon I might ride north and east and get the ferry to Stanraer, then ride up the west coast of Scotland and down the east. That would certainly meet your requirements in terms of scenery, water features and great riding. Coming south (spend a day or so in Edinburgh along the way) into northern England, there's a ferry from Newcastle to Amsterdam. From there I'd go south through Belgium (the Netherlands and Belgium are great to ride through, there's an easily-followed network of cycle routes that keep you off-road) into France. Down the Atlantic coast, taking in the Loire Valley on the way (chateaux, wine, great food, excellent campsites) and take in the Pyrenees on the France/Spain border. northern Spain is interesting, maybe ride as far south as Barcelona before turning north again. Across the south of France to the Alps, then into Italy from the north. If roman ruins interest you there is plenty to choose from, and there is great cycling all over the country. From there, maybe Austria and Hungary and then turn south and ride through the Balkans? Terrific scenery, not hugely expensive, takes you into Greece, Bulgaria, Turkey. Don't just stop at Istanbul, a loop down to Ephesus would take you to roman ruins the equal of anything in Italy.

That's just off the top of my head. You could devise a dozen equally interesting routes, including more of the northern European countries.