Suomenlinna

Suomenlinna is an 18th-century sea fortress and nature area with centuries-old artillery and defensive walls, spread across 6 linked islands. Walking trails cross parkland between popular sights like the King's Gate drawbridge and Suomenlinna Museum, which recounts military and maritime history. Submarine Vesikko lets visitors explore a restored 1930s vessel. There's also a brewery and several waterside restaurants.