Welcome to Siaröfortet
The ferry stop, Siaröfortet, is named for a fortress built here in 1916, when, after the outbreak of WWI, military authorities decided that the Vaxholm fortress just didn’t cut it. The fortress and its museum are the main draw, but the island is also one of several in the archipelago that was used as a cemetery (kyrkogård) for victims of cholera, and the graveyard site can still be visited.
There's also great swimming, canoes for rent, boules and a sauna (adult/child 95/60kr, book at the hostel). It's a popular stop for parents; kids can basically be turned loose on arrival, although the signs warning of barbed wire and other scraps of military history aren't kidding around.