The probable base/platform of a World War 2 pillbox on the cliffs at Challaborough Beach, Devon, England. Located just south east of the lifeguard station.
This platform is mentioned in this listing for a different pillbox: https://archaeologydataservice.ac.uk/archives/view/dob/ai_full_r.cfm?refno=6597
312 photos taken in August 2021 with a Sony a6000 and processed in Agisoft Metashape.