Lake Aussenalster in Hamburg, Germany rarely freezes over enough to allow tens of thousands to go skating on it. The ice has to be at leat 18 cm thick before officials declare it safe to walk on. The last time that happened was in 1997. This weekend it was thick enough to do so again.
This of course is because of galloping global warming. I have to point out that it hasn’t frozen completely solid – but solid enough for officials to give the green light for people to walk on without risk. Does anyone have the data on the years it has been officially opened?