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Neoclassical and romantic nationalism trend

Carl Ludvig Engel, appointed to plan a new city centre on his own, designed several neoclassical buildings in Helsinki. The focal point of Engel's city plan was the Senate Square. It is surrounded by the Government Palace (to the east), the main building of Helsinki University (to the west), and (to the north) the large Helsinki Cathedral, which was finished in 1852, twelve years after Engel's death. Helsinki's epithet, "The White City of the North", derives from this construction era. Most of Helsinki's older buildings were built after the 1808 fire; before that time, the oldest surviving building in the center of Helsinki is the Sederholm House (1757) at the intersection of Senate Square and the Katariinankatu street. Suomenlinna also has buildings completed in the 18th century, including the Kuninkaanportti on the Kustaanmiekka Island (1753–1754). The oldest church in Helsinki is the Östersundom church, built in 1754.

Helsinki is also home to numerous Art Nouveau -influenced (Jugend in Finnish) buildings belonging to the Kansallisromantiikka (romantic nationalism) trend, designed in the early 20th century and strongly influenced by Kalevala, which was a common theme of the era. Helsinki's Art Nouveau style is also featured in central residential districts, such as Katajanokka and Ullanlinna. An important architect of the Finnish Art Nouveau style was Eliel Saarinen, whose architectural masterpiece was the Helsinki Central Station. Opposite the Bank of Finland building is the Renaissance Revivalish the House of the Estates (1891).

The only visible public buildings of the Gothic Revival architecture in Helsinki are St. John's Church (1891) in Ullanlinna, which is the largest stone church in Finland, and its twin towers rise to 74 meters and have 2,600 seats. Other examples of neo-Gothic include the House of Nobility in Kruununhaka and the Catholic St. Henry's Cathedral.

In addition to other cities in Northern Europe that were not under the Soviet Union, such as Stockholm, Sweden, Helsinki's neoclassical buildings gained also popularity as a backdrop for scenes intended to depict the Soviet Union in numerous Hollywood movies during the Cold War era, when filming within the actual USSR was not possible. Some of them, including The Kremlin Letter (1970), Reds (1981), and Gorky Park (1983). was possible due to such Russian cities as Leningrad and Moscow also having similar neoclassical architecture. At the same time due to Cold War and Finnish relations with the USSR the government secretly instructed Finnish officials not to extend assistance to such film projects. There are some films where Helsinki has been represented on its own in films, most notably the 1967 British-American espionage thriller Billion Dollar Brain, starring Michael Caine. The city has large amounts of underground areas such as shelters and tunnels, many used daily as swimming pool, church, water management, entertainment etc.