What happens if a journey ends in a different city from where it started?

Regarding the validity of the voucher, the relevant city is the one where the journey started.

The promotion will take place in the following cities:
Hamburg, Hannover, Lübeck, Düsseldorf, Bochum, Bonn, Essen, Dortmund, München, Nuremberg, Ingolstadt, Frankfurt a. M., Wiesbaden, Darmstadt, Mainz, Offenbach, Berlin, Leipzig, Dresden, Stuttgart, Karlsruhe und Mannheim.

The city of Cologne is excluded from the promotion.