I don't miss much in this area !
A typical observation post on a RAF base. It's buried in the earth bank that forms the northern perimeter of RAF Sealand.
The earth bank is interesting in itself, it is actually the first sea wall that was built to start the land reclamation from the Dee estuary. It ran from Shotwick (just north of), to the Queensferry area. It is actually quite distinctive on Google Earth, and also contains the A548 pillbox on the road to the new bridge (near the electric pylons).
It's about here (really ?), it's in the vee of the bank, only just visible (
Raf Sealand O/P )
observation slit
And nearby, and old boiler (Lancashire or Cornish - don't ask me) used as a bridge: