I am now in the Brühl town of Cologne, Germany. I have visited almost all the attractions in Cologne, and I have also been to Bonn, including Beethoven’s former residence.

Bruehl is relatively far from Frankfurt and Munich. To go to Frankfurt and Munich, you need to change trains in Cologne.

In Bruehl, Cologne and Bonn are the first choices. Have you traveled all over? Cologne's hot springs, cruises on the Rhine, several large museums in Bonn, Koenigwinter's aquarium and castle, the former embassy district (look at the former Chinese Consulate). Cologne and Bonn still have a lot of tourism resources.

Also, have you visited all Bruehl’s own attractions? Have you gone to Phantasialand? Bruehl's most famous Fort Augustus and Fun Park have been visited.

From Bruehl, then head south to Koblenz. Or wander around North Rhine-Westphalia, the Ruhr area, Trier, Münster and so on.

Castles are relatively common in Germany. I don't know what you want to see. Closer to you, for example, there is the castle Schloss Drachenburg in Koenigwinter in Bonn. Although not as big and famous as Neuschwanstein Castle. But it is also a real castle.