The cheapest flight to Dortmund you can get by boooking 24 days before departure.
The most popular airlines on the route Warsaw - Dortmund: Lufthansa (LH), LOT (LO).
The cheapest flights you can book on the route Frederic Chopin (WAW) - Dortmund Airport (DTM).
There is no direct flight on the route from Warsaw to Dortmund
The shortest flights with change last about 3h 25min.