A tourist visits the monumental King's Gate of the island fortress of Suomenlinna in Helsinki, capital of Finland, on June 24, 2013. Fortress of Suomenlinna is a unique historical monument and one of the largest maritime fortresses in the world. Its construction began in 1700s when Finland was part of the Kingdom of Sweden. As an example of European military architecture of its time, Suomenlinna was included in UNESCO's World Heritage List in 1991. (Xinhua/Yan Ting)