The Deutsche Mark was replaced by the Euro currency almost ten years ago, but yet our local store Rompel still accepts our former currency for payment! I remember having seen the sign right after the Euro was introduced, but did not anticipate this promotion would last that long.
If you still have any Deutsche Mark hidden in drawers, forgotten coat pockets, under mattresses, or just tucked away in old letters – then go shopping at Rompel in Oberursel.

Deutsche Mark are still being accepted here! sign at the cash register
According to the Bundesbank, Germany’s state bank, only half of all Deutschmark coins were recovered following the introduction of the Euro, leaving the equivalent of a massive 3 billion Euros in circulation.
I’m not sure if they still offer this, but Main-Taunus-Zentrum used to exchange old DMs for MTZ vouchers.