That's a clever use for these flak towers and they look pretty cool. I guess its partly because those towers are difficult to demolish that they just went and thought to build on top of it.

Oh, absolutely. They did similar remodelings with 2 or three old civil defence bunkers here in Frankfurt, albeid on a much smaller scale.

Some where demolished but it always took multiple quite serious tries
We talk about highrise sized bunkers.
Type 1 , like this one had a wall thickness of 3,5 meters and roof was 5m . . .

And to quote someone who spend months beating a hole in some old shelter of the same time
"Forget the concrete of today , it doesn´t hold the water to the old ones "

At least you know with these it's never going to fall down on its own!

For sure
I remember that the one at Hamburg-Wilhelmsburg was blown by the british , the pictures taken it looks liek a rocket that wanted to fly off with all the smoke coming out of the windows .
They managed to convert the inside to a gigantic hole . . . you will find that its still standing just recently got converted .

Build to be able to take direct hits and they did .
I remember the interview of an old man who used to be a boy helping to operate the guns as he recalled that men were blown of them of the blasts .
The soviets also managed to get some casle siege out of some in berlin , but found out that their guns could only scatch them .

A great example of "turning swords into ploughshares".
Are those high-rise garden plantings I can see on the upper levels?

Yeah, they have extensive terraces on top.