I've uploaded some pics to
mparaz @ flickr. Apologies to the poor quality, I am no photographer.
Some stuff I've done:
walked around - it's nice to walk and you don't feel tired when it's cool;
tried the different urban transit systems - bus, Straßenbahn (streetcar) and Stadtbahn (light rail transit);
visited the Altstadt (old town) with the "world's largest pub" - streets and streets of outdoor pubs/restaurants;
visited the Königsallee - high end shopping avenue;
went up the Rheinturm (Rhine Tower), 168 meters above the Rhine with a great view of the city;
ate bratwurst mit brötchen (in bread), döner, schnitzel, turkey, fish & chips;
drank some Altbier (which had a nasty bitter aftertaste), gotta try others;
... and of course, work stuff, what I came here for!