Hint: Capital is the municipality that serves as the seat of government for a department, nation, state, province, or other administrative areas. It is usually a city that contains the government's offices and meeting places; its status as the capital is also determined by law or constitution.
Sofia is the European Union's 14th largest city. It is bounded on 3 sides by mountains: Vitosha on the south, Lyulin on the west, and the Balkan Mountains on the north making it Europe's third-highest capital after Andorra la Vella and Madrid. Sofia has been named as one of the top ten best places in the world for start-up companies, especially in the information technology sector.
Sofia is Bulgaria's capital and largest city. The city is situated in the western part of the nation, at the foot of Mount Vitosha. As a commercial, manufacturing, transportation, and cultural center, it is strategically located in the heart of the Balkan Peninsula.
As Bulgaria's capital, Sofia is home to many of the country's foremost universities, cultural institutions, and commercial enterprises. The "triangle of religious tolerance" has been coined to describe the city. This is due to the fact that Sveta Nedelya Church, Banya Bashi Mosque, and Sofia Synagogue are all located within one square, representing three major world religions: Christianity, Islam, and Judaism. The Catholic Cathedral of St Joseph was recently added to this triangle, making it a "square."
So, the answer is Bulgaria.
Note: The Sofia Valley's geographic location restricts the passage of air masses, raising the risk of particulate matter and nitrogen oxide emissions. That is, Sofia's air pollution levels are among the highest in Europe.