Japan's Crown Prince Fumihito and Crown Princess Kiko visited the Hagia Sophia Mosque in Istanbul on December 5.

The imperial couple are on their official visit to Turkey.

Hagia Sophia was originally built as a Christian cathedral about 1,500 years ago.

The structure became an Islamic mosque during the Ottoman Empire and is the fourth largest cathedral in the world.

The crown prince and princess asked their guides questions about the mosque's history and decorations.