Helsinki, the capital of Finland, is often called the 'White City of the North' because many of its prominent neoclassical buildings are constructed from light-colored local granite. Founded in 1550 by King Gustav I of Sweden to rival the trading power of Tallinn, Estonia, the city evolved into a sophisticated urban center under both Swedish and Russian influence. One of its most famous landmarks is the green-domed Helsinki Cathedral, which towers over Senate Square. Helsinki is unique for its relationship with the sea, being built on a peninsula surrounded by over 300 islands. It is also famous for its 'underground city'—a vast network of bunkers and tunnels carved into the bedrock that house swimming pools, shopping centers, and emergency shelters for the entire population. As the coldest capital in the Nordic region, Helsinki has mastered winter life, featuring heated sidewalks in the city center to melt snow and a culture where saunas are considered a basic human right, with over 3 million saunas existing for a population of 5.5 million people.