Since there are ‘Muttertag’ and ‘Vatertag’ comnig in Germany, Lufthansa is giving away  20€ voucher codes here.

The basic T&Cs are:

• Only for flights departing from Germany
• Book between 2016-04-23 and 2016-07-23
• Travel between 2016-04-32 and 2016-10-23
• Limited to 1 code per mail address

If you get an error stating “no more vouchers available” try again the following day. It seems as if there is a daily limit.