I've driven past here lots of times, wondered about the green building, thought it looked a bit like a public convenience but wondered why. You guessed it, today I stopped and looked around. At last I got the picture. I must add that I didn't undertake a full investigation so as usual with these structures, you get what you find and whether you decide to accept the convenience or give it a miss depends very much on . . . well, you get the picture.
The cache is not on, under or in the structure (of course) but is in a much more friendly place, 46 metres away on a bearing of 175o. If you have any problems with the calculation just go look under a tree that is approximately 46 metres upstream.
Please replace as found.