Rome is the capital city and a special comune of Italy. Rome also serves as the capital of the Lazio region.  It is the center of the Metropolitan City of Rome, which has a population of 4,355,725 residents, thus making it the most populous metropolitan city in Italy. Rome is located in the central-western portion of the Italian Peninsula, within Lazio (Latium), along the shores of the Tiber. The Vatican City (the smallest country in the world) is an independent country inside the city boundaries of Rome, the only existing example of a country within a city: for this reason Rome has been often defined as capital of two states. Its average annual temperature is above 20 °C (68 °F) during the day and 10 °C (50 °F) at night. In the coldest month, January, the average temperature is 12 °C (54 °F) during the day and 3 °C (37 °F) at night. In the warmest months, July and August, the average temperature is 30 °C (86 °F) during the day and 18 °C (64 °F) at night. Rome today is one of the most important tourist destinations of the world, due to the incalculable immensity of its archaeological and artistic treasures, as well as for the charm of its unique traditions, the beauty of its panoramic views, and the majesty of its magnificent "villas" (parks). Among the most significant resources are the many museums – Musei Capitolini, the Vatican Museums and the Galleria Borghese and others dedicated to modern and contemporary art – aqueducts, fountains, churches, palaces, historical buildings, the monuments and ruins of the Roman Forum, and the Catacombs. Rome is the third most visited city in the EU, after London and Paris, and receives an average of 7–10 million tourists a year, which sometimes doubles on holy years. The Colosseum (4 million tourists) and the Vatican Museums (4.2 million tourists) are the 39th and 37th (respectively) most visited places in the world, according to a recent study.