This may be of interest to some, during WW2 there were a number of forts erected in the Thames Estuary, this being the main river running through London, UK., intended as a defence against German attack by air or sea. After the war they fell into disuse although for a while used by pirate radio station. Sadly, although of historical significance the sea air has taken its toll and they are considered dangerous structures now, although there is apparently some charitable scheme to attempt renovation. May be just one will be chosen, who knows.
Never ceases to amaze me what can be achieved so quickly in war time yet during peacetime takes forever or of course, no money.
https://youtu.be/1jbbNLadH74?si=tSVv3yiLqmiL0s03
Geffers