Strathcona Ave, Clapham, just beside the entrance to Balyana Services. This one took a little while to find as it was under a significant amount of soil. I was walking the dog past here for months before it got opened up. Eventually a surveyor dug it up to make use of it (hence the white spray paint on the centre dot).
I think difficulty on this one was 2, but Terrain still 1 as it on the footpath. Muggle factor 1 as no-one stops to watch people on the road here.