Wednesday autumn colours before a grey sky, seen from a subway station
Yesterday, clear blue skies. The building may be an old powder magazine, but I'm not sure.
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Edit: I just leaned from a book I'm reading that it's not a powder magazine, but an air raid bunker. There are 10 such bunkers in Hamburg and they are called Zombeck-Tower after their designer, Paul Zombeck. You can see the inside of such a bunker here