Sea forts

Suomenlinna (), or Sveaborg (), is a sea fortress composed of eight islands, of which six have been fortified. Located about southeast of the city center of Helsinki, Finland, Suomenlinna is a popular destination for both tourists and locals, who enjoy it as a picturesque picnic site.

Spanish peninsula claimed by Morocco

fort in Charleston, South Carolina

fort in Charente-Maritime, France

island group

Murud-Janjira () is the local name of a fort and tourist attraction situated on an island just off the coastal town of Murud, in the Raigad district of Maharashtra, India. Malik Ambar is credited with the construction of the Janjira Fort in the Murud Area of present-day Maharashtra India.'''''' After its construction in 1567 AD, the fort was key to the Sidis withstanding various invasion attempts by the Marathas, Mughals, and Portuguese to capture Janjira.

islet in the Philippines

thumb|Pampus island prior to restoration in 2004

Island fort in Arabian Sea off the coast of Western India

fortress built to defend the city Gothenburg against the Danish fleet

Khanderi (officially Kanhoji Angre island) is an island with a fort, located south of Mumbai, along the coast of Maharashtra, India.

small, fortified towers built in the Thames and Mersey estuaries

fortified island in Florida, USA

Middelgrundsfortet (), known as Ungdomsøen (The Youth Island) since 2015, is a sea fort located on an artificial island in the Øresund between Copenhagen and Malmö. The fortress is constructed at a point where the seabed is 7 meters below the water surface at the northern meeting point of the straits Kongedybet and Hollænderdybet. Ferries connect Middelgrundsfortet with Langelinie, Copenhagen.

Flakfortet, meaning sand-shoal fortress, is a sea fort located on the artificially built island of Saltholmrev, in the Øresund between Copenhagen and Saltholm. The island and fort are simply known as Flakfortet; the name of the island; Saltholmrev, meaning the reef near Saltholm, is seldom used.

building in India

ancient monument in Copenhagen Municipality (151218)

heritage-listed former penal site and defensive facility in Sydney Harbour, Australia

group of two small islands off the coast of Normandy, France

fort in Ille-et-Vilaine, France

Maunsell navy fort off the coasts of Suffolk and Essex, United Kingdom

well listed by the Institute of Artistic and Cultural Heritage of Bahia in the city of Salvador, Bahia

fortification built off shore in Bourcefranc-le-Chapus in the department of Charente-Maritime, France

fort built on a small island in Milford Haven, Pembrokeshire

fort located in Vijaydurg

building in Norte Region, Viana do Castelo District, Portugal

fort in Plougonvelin, in the Department of Finistère, France. It is located on a tidal island

fort located on the coast of the Strait of Dover, northern France

fort near Kronstadt

sea fort located in the Solent, near Portsmouth, England

fortress in San Juan, Puerto Rico

island in Ille-et-Vilaine, France

island in Victoria, Australia

lighthouse east of Isle of Wight, UK