The flak towers were built by forced labour. On the walls inside you can still see graffiti, written in chalk and pencil, by prisoners of war.
“Milano, poi morire” wrote one Italian prisoner. “Milan, then die”.
Today one of the flak towers houses an aquarium and another is used by the Austrian army. But there is controversy about what should be done with the others.
Getting rid of the reinforced concrete hulks would be too difficult and expensive, according to Sandro Forst of the Vienna City Administration.
“Even if you put a bomb inside you couldn’t destroy the tower so you would need very strong diamond saws to cut it into pieces,” he said.
“And to cut up a whole tower is, from a technical point of view, impossible.”
The towers have few windows and their cold concrete halls and echoing stairwells recall a period in history that some Austrians would prefer to forget.