Undemolishable

While strolling through beautifull Augarten in Vienna, you encounter this eery sight. It's a flak tower built be the Nazis to defend Vienna from allied bombers. Apparently, Hitler took a personal interest in the design and function of these behemoths. I think it shows. Because of the diameter of their massive concrete walls - 5 meters on average - they are considered to be undemolishable and left standing as an uneasy memento. There are five up to these days in Vienna - some are empty, some have been put to new uses, e.g. as Museums.