the Stiftskaserne flakturm is still used by the military and you can't take pics of it
It is the partner tower to the L turm that I posted first, the one that has been converted to an aquarium and climbing tower. it's about 400m away from it inside a big barracks and is as far as I know a NATO/Austrian command center.
The Stiftskaserne flakturm cannot be viewed from street level but if you are lucky enough to go on the prater wheel it is quite visible on the horizon, though the augarten towers are much nearer and more dramatic
