Please be away that even though you have booked a Topdeck tour there will still be people who want to go out partying. As I said to Dayna above, just enjoy the trip you want to do and there will always be other people who will want to just enjoy quiet nights like you.
Your question is quite hard to answer because I would love to go back to all the places I have visited. I have not explored any of Spain except for Barcelona and would love to do more of Spain. I have also never been to Portugal but I have a couple of friends who have just returned from travelling along the coast of Portugal and absolutely loved it. Unfortunately I cannot provide you with any recommendations for that part of Europe.
From my experiences I really enjoyed sailing through Croatia and seeing all the little islands. That was definitely a must see for me. Also I have always been a massive fan of Germany so on my last trip we stayed in Munich and based ourselves there. Munich itself is amazing and has heaps to do (English Gardens, Science Museums, Glockenspiel, Marienplatz, beer halls, palaces, bike tours etc.) but is also located in the Bavaria region of Germany. I found Bavaria to be one of the most beautiful regions in Europe and from Munich you are able to do day trips to Neuschwanstein Castle (the castle they based the Disney Castle off) and Zugspitze which is Germany's highest mountain and Lake Starnberg and the five lakes region just to name a few. From Munich you can easily get the train and do day/overnight stays in places like Salzburg and Innsbruck as well. Nearly all of the Bavarian Alps and it's little towns look like you are walking into a postcard. If you are into hiking or the outdoors like me the Bavarian Forest is the oldest national park in Germany and has some spectacular walks.
If you have time I'd highly recommend Munich and the surrounding Bavarian areas.
There is so much I could recommend but I'll leave it at that for now before I get too carried away haha.
I hope this helped.