17. Mecca, Saudi Arabia
Source: Iconosquare
Mecca offers a variety of reasons to visit. However, during hajj, which means pilgrimage, the number of people visiting the city triples it’s population of about 2 million. The city is home to a number of archaelogical and historical buildings including the Ajad Fortress. It’s one of the most important locations to the Muslim community and is considered the holiest city in Islam. It receives about 7.5 million visitors each year.