Suomenlinna, or Sveaborg, is the sea fortress on a series of islands near Helsinki. Work on the fortress began in the 18th century, and today is considered a UNESCO World Heritage Site. People actually still live there! The district of Suomenlinna has a population of 800 permanent residents. Nathanael and I had a blast trying to find all of Suomenlinna’s secrets. A fair number of the doors and tunnels have been left open, so the public can wander freely through the rooms and passages. There are also a couple of cute cafes and museums on the island to round out the whole experience. This is one of Helsinki’s most popular tourist sites, and it’s definitely worth a visit!