Fort Henry is a long reinforced-concrete observation bunker hidden in the cliff edge above Studland Bay, half a mile north of Old Harry Rocks. It was built in 1943 by Canadian engineers as a viewing point for the dress rehearsal of the D-Day landings — the assault force exercising on the beach below included troops, tanks, and naval gunfire support. Senior commanders, including Eisenhower, Montgomery, and the King, watched from inside.
It is a short detour off the South West Coast Path between Swanage and Old Harry, freely accessible at any hour, with an interpretive panel and an unrestricted view down the beach. Bring a torch — the interior is dim. One of the more unexpected sights on the Purbeck coast and an essential stop for anyone interested in the Second World War.