Harwich Redoubt is a circular fort built in 1808 to defend the port of Harwich, Essex from Napoleonic invasion. The Harwich Society opens it to the public.
Wikipedia https://en.wikipedia.org/wiki/Harwich_Redoubt
Official Website https://harwich-society.co.uk/heritage-trail/redoubt.htm
Address Harwich CO12 3, United Kingdom
Coordinates 51°56'31.071" N 1°17'20.256" E