This is geohashing:
Monkey & I parked in a layby and wandered down a small stone path. The field containing the co-ordinates was private, so Monkey & I pushed our way through the stinging nettles up to the edge of the boundary fence:
The official geohash page is here.
Monkey and I are going to try and reach the Birmingham East geohashes for the next week. No guarantees, but wherever possible.