In reply to 1906johns:
when I lived in Nottm (long long ago) it was the other place to train.
Big retaining wall behind the football pitches on the Forest.
Looked completely unused when I looked last summer & not even maintained ie pointed.
If it should collapse (which didn't look unlikely) while you were climbing it really would ruin your day
I'd guess it's holding bacj several hundred tons of soil.
Shame! it used to be good for loong stamina sessions.