Cologne activities

https://community.ricksteves.com/travel-forum/germany/can-i-see-enough-of-cologne

Walk up the tower of the cathedral! You get great views of the area.

My wife and I just spent four days in Cologne this past weekend. Our highlights were the Cologne Dom (take a guided tour of the interior) and the Lindt Chocolate Factory (stop in their cafe for something made of chocolate - we had mousse cake). Both sites are easy to get to. The Dom is just outside the main train station and Lindt is a nice 15 minute walk along the river promenade south. In between are loads of good restaurants serving classic German fare as well as other cafes, ice cream spots, bakeries, etc. Just steps west of the promenade are several pedestrian zones with shops and more restaurants. Another suggestion is an hour long Rhine cruise or walk along the southern edge of the bridge that crosses the river. The fencing is coveted with love locks. Look for the one that says "Ellen and Bill 11 October 1986." We just added that ourselves.

Just did a day trip to Cologne last week. Went to Dom, Lindt factory, with an excellent lunch at Brauerei zur Malzmühle in between. Fit in some shopping in that area as well. Had more Kolsch at Peters before we left. Kolsch might have been my favorite beer type this entire Germany trip.

Agree with what all previous posts have recommended. And, if you want to spend time indoors, then the Wallraf-Richart Museum https://kunstfreunde.koeln/
and the Roman Museum (in it's temporary location)
https://www.roemisch-germanisches-museum.de/Startseite are excellent.