The coordinates above are not leading to the cache.
Before looking for this Bonus, you have to solve the adventure lab:
Diekirch an aftermath of the war reloaded.
Here are the coordinates: N49°53.EAB E006°08.CFD
Use your phone's native QR code scanner to open this adventure in the Adventure Lab mobile app, or share the following URL:
https://labs.geocaching.com/goto/Diekirch
