Suomenlinna (Finnish), or Sveaborg (Swedish), literal translation Finland Castle, until 1918 Viapori (Finnish), is an inhabited sea fortress built on six islands and which now forms part of the city of Helsinki. Suomenlinna is a UNESCO World Heritage site and popular with tourists and locals, who enjoy it as a picturesque picnic site. Suomenlinna is now one of the most popular tourist attractions in Helsinki as well as a popular picnicking spot for the city's inhabitants. On a sunny summer day the islands, and in particular the ferries, can get quite crowded. In 2009, a record 713,000 people visited Suomenlinna, most between May and September. A number of museums exist on the island, as well as the last surviving Finnish submarine, Vesikko.