Discovered at the Geocaching Alstervergnügen
Alstervergnügen is an event in Hamburg which only happens when the alster lake is frozen so that several hundred thousand people can go on the lake. The last time it happened 10 years ago. This year it "almost" happened. The ice was thick enough, but there were too many air bubbles in it to allow everyone to go on it. Therefore the Alstervergnügen was not officially happening. However, fearless cachers had this gathering on the ice