Who knows what to do with it? In Vienna too, the huge Flak towers are still standing (a great buzz for me!). They tried to demolish one after the war, and nearly wiped out the nearby buildings instead - the walls are typically about 6 meters thick.
When I was last there, most had been turned into museums, terrariums/ aquariums, and rock climbing walls, with a single example being retained by the MoD, having direct underground access to Parliament.