Germany like many other countries ask for proof of the return ticket that you leave them. Why? They want only serious people on their country who commit to the visa rules. This doesn't mean you need to buy a real ticket you can use utilize the use of a dummy ticket and buy only one-way ticket to Germany. The officer will let you in this way.
Aachen/Merzbruck Airport - AAH
Altenburg Nobitz Airport - AOC
Augsburg - Muehlhausen Airport - AGB
The Germany officers ask 98% of the time for a Spain ticket pdf back to your country. you gotta bring a return ticket and if not use a dummy ticket to secure your flight and your way to this wonderful place.