While most Bundesliga clubs enjoy close links with their fans thanks to their ownership structures, FC Union Berlin share a particularly unique relationship with their loyal followers.
In 2008, supporters of the 2. Bundesliga side donated 140,000 hours of their time to help modernize their home, the Stadion An der Alten Försterei ("Stadium near the old Forester's house"). In 2004, they even sold their own blood to cover a €1.5m debt in order to keep their professional status.
On Sunday, thousands of Eiserne fans gathered on the terraces of the stadium they helped build to sing and drink for 90 minutes. This sounds like a typical occurrence, except for the fact that it is currently the winter break in Germany and there are no games.
Fans were gathering for the tenth annual Christmas event, a tradition that sees thousands of Union Berliners drink Glühwein (mulled wine), wave candles around, light flares (obviously) and belt out a combination of Christmas tunes and football chants.
The Guardian interviewed Union Berlin fan Torsten Eisenbeiser, who came up with the idea a decade ago:
"After a couple of bad games we, who always stand together during the games, just went home without wishing each other merry Christmas. I suggested to one friend that we should get together in the stadium the day before Christmas Eve and sing some Christmas songs."
The yearly event started as an unofficial gathering to which just 89 fans showed up. Last year, 17,000 people attended, including players and supporters of other teams from around Germany and the rest of Europe. The video and images above suggest similar numbers turned up at the 19,000 capacity stadium for the 2012 festivities.