I ultimately found one walking tour in the region, in Bonn to be specific. The website is here.
As the details are buried in a PDF I'll quote them here.
Bonn - Roman Settlement, Baroque Residence and Beethoven City
Discover Bonn´s numerous sights on a walking tour through the
historical city centre
The historical centre of Bonn offers an abundance of sights which are
easily reached on foot. The major points are the Beethoven monument,
the romanesque Minster Cathedral, the Electors palace (nowadays the
University) with the elegant Hofgarten and the baroque City Hall. The
tour also takes you to the banks of the Rhine, near the Opera, from
which river excursions on the boats of the Weiße Flotte (white fleet)
are possible. The imposing view of Germany´s oldest nature park
Siebengebirge (seven hills) can be seen from the banks of the Rhine.
The tour ends at Ludwig van Beethoven‘s birthplace in the Bonngasse.
Here you have the opportunity to visit Beethoven´s birthplace with the
Digital Beethoven House on your own. The entrance fee must be paid
separately at the Beethoven House.
Date and Time: Saturdays from 27 April to 26 October at 11 am
Meeting place: Bonn-Information, Windeckstraße 1/ am
(nearby Minster Cathedral Square)
Duration: around 1 ½ hours
Price: Adults 9 €, with reduction 5 € (children aged 12-17, students, disabled)
I didn't find out until after I payed, but tour is actually conducted in German and also in English if there are English speaking people joining the tour. As I was the only English speaker in the tour it felt a bit awkward, but the tour was still very interesting and I would recommend it.