Mystery Structure in the Photo Gallery

Hope you've all had a look at that in the Photo Gallery/Old Ridgewell Photos. Firstly I have no idea what this mystery structure can be. When looking at photo "structure 22" on Page 6 in the album I'm guessing the windowless and doorless walls are around 6ft on the wall at lower end of the photo but looking at the wall higher in the photo it looks taller (is the floor lower?) and those centre walls - they look quite purposeful, as if they are meant to hold something (which is repeated again but higher in the end wall as can be seen in photo structure-01) . Top right (photo structure 22) - I can't make my mind up if its being knocked down in some part or it has a purpose made curvature repeated throughout.
Something left behind by the RAF perhaps, though it looks as if it has not been there that long going by the bare earth with just a bit of grass growing beside it. We can see in other photos that paths have been put in or worn to other areas but this has (as far as I can see) nothing leading to it. Is it abandoned? The orientation of it suits the surrounding buildings. Being brick it is a permanent structure. Any thoughts?

I have another mystery question as well, but felt odd about posting it. From many arial views you can see a heart shaped berm in the current photo's. Was this a recent landscaping design or was it present during the war. And if the later, to what purpose?

Thanks Chip