Discover Istanbul's architecture, history, and faith in some of the city's most beloved places of worship on a half-day walking tour. Start from Hagia Sophia, originally a Byzantine Orthodox Christian cathedral transformed into a Catholic church, mosque, and museum over the years. Head next to the Blue Mosque built by Sultan Ahmed I in the early 1600s, known for its stunning blue tiles and intricate designs. Conclude the tour at the Suleymaniye Mosque, once the largest mosque in Istanbul.