Because I had a cheap ticket I had 2 changes on my train to Cologne, but it wasn’t that bad. I arrived about 3pm.
Since all the hostels were full or expensive I went to the campground. It’s a reasonable distance from the city centre. Take the U-Bahn (which turns in to a street-level train after a few stops). After all my time in the East I was struck by how run-down the train looked here.
Go over the bridge (very wide, especially when you’re carrying a pack) and turn left. There’s another campground to the right, but it’s not as good. The official city campround is right on the bank of the Rhine and has free gas cooking! Finally! Showers are €0.50.