Pillboxes are concrete dug-in guard posts, normally equipped with loopholes through which to fire weapons. The originally jocular name arose from their perceived similarity to the cylindrical and hexagonal boxes in which medical pills were once sold. They are in effect a trench firing step hardened to protect against small-arms fire and grenades and raised to improve the field of fire. (Credit Wikipedia)
Please ensure you keep to the public right of way alongside the riverbank and do not stray onto the adjacent golf course. Ensure that children and pets are well supervised alongside the river, the bank is steep in places and the water is deep.