At this fortress-turned-museum you can check out the officers’ mess, kitchen, sleeping quarters and tunnels, plus two impressive 15.2cm cannons (they’re trained on passing Viking Line ferries!). Guided tours are available through the STF hostel at 1pm Monday to Thursday, 12.30pm Friday, noon Saturday, and noon and 3pm Sunday. There's also an audioguide (additional 95/70kr). It's free to scramble around the exterior of the fort.
Siaröfortet Museum
Stockholm Archipelago