A very large concrete pillbox.A galleried entrance,leading to a ring of firing positions,with a central elevated access.In reasonable condition.In the image,at either end of the pillbox,on the horizon,can be seen two towers.The lhs is that of St.John's Church,Epping,whilst the rhs,almost obscured by the bush,is a red brick tower,on Epping High Street,once a water tower.
see http://en.wikipedia.org/wiki/British_hardened_field_defences_of_World_War_II