Went for a detour to a reservoir this afternoon:

A lot roomier than I thought


This was one of two beds - the other one was just a sheet with some cardboard but this was a serious setup


This was sitting on a ledge between the two beds

The chamber of secrets


Didn't get many photos of the main room, my camera was quickly running out of battery. Some kids were skating in there and after a while a security guard came. I just can't believe this is all right here and I have never noticed.
I have a few questions though:
For those that had been before the renovation, how far does that air raid shelter go?
Also, from this map (Link removed - Admin), it says 7 of the marked single bunkers (dots) were built, and considering this one (one of the squiggles) was also built, do any of the others still exist? I get the feeling that even if the single ones do exist they are just gonna be sitting underneath people's backyards with not a lot to see.
Similarly, how do currently used reservoirs behave in terms of water levels - eg is there anything special to be careful of?