Better known as the Blue Mosque, the 17th-century Sultan Ahmed Mosque in Istanbul is often overshadowed by the nearby Hagia Sophia in terms of global recognition. However, it is definitely a destination everyone should see at least once in their lifetime. Considered the last great mosque built in the classical period of Ottoman architecture, it has five main domes, eight secondary domes and six minarets, as well as 200 stained glass windows. The mosque’s interior is decorated with hand-painted blue tiles, and its blue and white exterior is further lit up by blue lights at night.