Biking to the fabulous rock gym we were puzzled by this giant hunk of concrete. As we learned it was originally designed to assist the Führer’s troops in picking allied planes out of the sky before reaching Hamburg. This 1,860,867 ft^3 cubezilla now serves peaceful purposes. As the Energy Bunker, it stores thermal energy inside and has photovoltaic panels on top. We won’t pass judgement on the idea of harvesting the sun in usually cloudy Hamburg.