A lot of LCC´s, Low Fare carriers and charter operators in Europe publish their fares on international flights as "one-way fares" (and there´s no need to combine them into roundtrips - I´ve do that on flights from Germany to Spain quite frequently). This is NOT limited to countries within the Eureopean Union ! It is easily possible to book one-ways like MUC
- TBS i.e. one-ways into countries that require to obtain a visa upon arrival or upfront.
It is also very easy to book oneways into Turkey (no visa required).
Most Legacy carriers still do have the opinion that anybody willing to travel international as oneway will do so for business reasons and thus they assume it will be okay to charge a premium for that ...
Carpe diem ! Life is too short to waste your time ! Keep in mind, that today is the first day of the rest of your life !