Aleksanterinpatteri is a historic casemate battery on Vallisaari; from its courtyard and the observation deck built atop the structure, visitors can take in the island’s fortified landscape. From the top, visitors can enjoy views of the Helsinki archipelago, the city’s shores, and the open sea. The site is part of the island’s marked Aleksanteri Trail. This notice applies to the outdoor area and the observation deck; the interior of the building is not open to the public. Visitors must stay on the marked trails on the island, and the southern part is closed to the public. The 2026 water bus season has ended. If arriving by private boat, use the Torpedolahti guest harbor; contact information is provided in the boat arrival inquiries. Check the harbor’s policies before your trip.