Let's spend an afternoon in Düsseldorf on 30.04 (Sunday) - there is a lot to photograph and of course cafes for a refreshing drink afterwards. Sumanta has suggested the harbour - and more suggestions are welcome! Altstadt is another possible destination, for example.
There is an RE 10518 (https://reiseauskunft.bahn.de/bin/traininfo.exe/en/777066/463478/453380/32332/80?ld=15046&protocol=https:&seqnr=6&ident=lx.02763546.1492372356&date=30.04.17&station_evaId=8000044&station_type=dep¤tReferrer=tp&rt=1&rtMode=DB-HYBRID&) train which departs Bonn Hbf at 13.01 and Köln Hbf at 13.31 and arrives in Düsseldorf at 14.01. (So, we will meet a little after 14.00.)
It seems the marathon will not have completely finished, but it could give us some unexpected subjects. (For those new to Germany, you might want to find out about privacy laws, as these affect street photography. or bring model releases along if you want to publish images in which faces are recognisable.)
All are welcome - as always, please do update your RSVP as the time gets closer, so I know how many to expect. Thanks!