Day Trip to Rüdesheim, Koblenz
Visit the Siegfried's Mechanical Instrument Museum.
It sounds strange but this place is great! It's actually in a town called Rudesheim not too far from Koblenz.
The instruments are amazing! You can only visit by guided tour but it is well worth it.
If you are interested in music or anything mechanical then you will love this place. I'm not into either of those things particularly and I still really loved it there.