Completed in 1968, Battery Arholma was a top-secret part of Swedish defence - built to stop a possible invasion from the east.
Behind the big 10.5-centimetre gun, still looking out to sea, lies an underground world. It contains accommodation, kitchens, medical facilities, a power generator room and a battle control centre - everything needed for 340 men to live and defend the coast in the event of war.
Today, the battery is only shown through guided tours - a unique opportunity to step straight into Swedish military history.
Arholma can be reached by Waxholm boat from Stockholm and pass boat from Simpnäs all year round. There is also a guest jetty on the island for those who come with their own boat.
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