When we visited the Devil's Dyke in 2019 I noted this ruin on the horizon. From the looks of it and based on what else I've seen I had this down as either a relic from the feared Napoleonic invasion [which thankfully never happened] or more probably a leftover from WWII [Sussex is littered with different examples]. Only now have I discovered that more unusually this dates from the Great War. It was known colloquially as "The Bomb House", but its purpose was not rediscovered until 2012. Built in 1918 it had steel lined walls to enable the testing of bomb detonators to be carried out. With it being put into action so near to the armistice it only saw a short period of service before being abandoned.