There was an IB flash sale for MAD-DUS Nov 27-30 for 100eur.
Outbound arrives at DUS Wed night 22H30 so planning to stay at the PI near the Dusseldorf-BF for 68eur.
Thu morning head to Cologne for sightseeing and xmas markets, staying at the PI there that night for the 57eur rate.
Fri head to Bonn, hotels at Bonn that night are OK, at Cologne it's very high, but Dusseldorf Melia/Melia Innside is 110/61 so will head back up to Dusseldorf that night.
Sat sight see Dusseldorf and fly back that night....all quite cheep and cheery inline with the flash sale.
Am I missing anything?