Hamburg's "underworlds" bunker tours

Like
Berlin and other cities,
Hamburg too has its
WWII air-raid shelters and
Cold War nuclear bunkers, some of which can be visited by tourists on specialist guided tours. The Hamburg equivalent to the "
Berliner Unterwelten" association is called "
Hamburger Unterwelten", and there is even a second such organisation called "
unter Hamburg" (literally 'under Hamburg' – also quite apt).
Both offer various tours of different sites. Unlike their Berlin-based counterpart, however, they do not offer regularly scheduled tours that you can simply turn up for. Instead all tours have to be signed up for in advance – well in advance: they often book out weeks or even months ahead of their scheduled date.
As regards costs: the normal tours (in German) with both associations cost in the region of 5 to 10 EUR per person; specially arranged English-language tours are likely to be more expensive. I haven't been on any of their tours yet, as I haven't been to Hamburg long enough in recent years, and their tours tend to book out so far in advance. But hopefully one day I will be able to give a first-hand report here.