I think you can travel free on local S-bahn trains, but I'm not sure if Köln - Dortmund would exceed the limit (in terms of km), do you have the tickets already ? It will probably say what the terms and conditions of the free travel are - I can translate it if you want? Or if not there should be some sort of symbol of the free transport like a "DART" or "Tube" logo - for Stuttgart it's the VVS (http://de.wikipedia.org/wiki/Verkehr...bund_Stuttgart) which is the metro area of Stuttgart (would be like free trains, buses and DART within County Dublin for say a Shels match), this is the one for Dortmund Area (Rhein/Ruhr), maybe contact them and ask them to confirm it.
http://www.vrr.de/en/contact_us/index.html
Bookmarks