Bonn / Cologne in February

For Cologne, we really enjoy staying at the Coellner Hof Hotel. Lovely rooms and fantastic breakfast buffet.
http://www.coellnerhof.de/default.aspx?lang=en

You arrive after Ash Wednesday, so will miss the craziness of Karneval in Cologne. The city has much more to offer than just the cathedral, as this was a huge Roman city as well as the home of one of the most important Arch Bishops of the Holy Roman Empire.

Since Rick doesn't cover the city very well, nor Bonn either, check out attractions and tours on Trip Advisor.
http://www.tripadvisor.com/Attractions-g187371-Activities-Cologne_North_Rhine_Westphalia.html

"13 February (Saturday) we will spend sightseeing in Bonn... Suggestions to see in both Bonn and Cologne?"

How about NEAR Bonn?

Here's an alternative or possibly an add-on outing... An hour's scenic train ride into the MIDDLE RHINE VALLEY (UNESCO World Heritage status) gets you to the old-world town of BRAUBACH where you can tour the only never-destroyed medieval Rhine castle - MARKSBURG

MARKSBURG visitor information

The Rheinland-Pfalz ticket day pass (€28/2 adults) covers the train journey using the regional trains. Regional express trains depart Bonn's main station hourly at :57 after the hour for Koblenz, where you have a layover of 12 minutes for the train to Braubach.

The walk up to the castle requires about 20 minutes, the tour one hour. Altogether you might allocate 4.5 - 5 hours for this outing.

In Bonn, I can say there is one must: Haus der Geschichte (House of the History). It is extraordinary, just splendid musuem of contemporary history.
In Cologne: cathedral, Cologne’s Old Town, Hohenzollern Bridge with love padlocks are not to be missed.