Hagia Sophia (Ayasofya), Istanbul (must see)

Hagia Sophia is the ultimate overachiever of both architecture and religion. Built in the 6th century for Emperor Justinian I, it began life as a grand Christian cathedral—basically the power seat of the Eastern Orthodox world. Its giant dome was such an engineering feat that people said it hung from heaven by a chain. At 180 feet tall and 100 feet wide, it still gets a lot of impressed neck-craning today.

Still, history wasn’t satisfied with just one identity for Hagia Sophia. When the Ottomans conquered Constantinople in 1453, Sultan Mehmed II turned it into a mosque. Up went the minarets, out came the church bells, and Christian images were masterly covered—like someone switching décor for a very different house party... Today, you’ll see a fascinating mash-up: Islamic calligraphy panels right beside shimmering mosaics of the Virgin Mary and Jesus. History lesson and cultural fusion rolled into one.

Inside, look for the famous Deësis mosaic from the 13th century, featuring Christ, John the Baptist, and the Virgin Mary, expressing emotion so well it almost feels like they’re watching you back. And don’t miss the “wishing column.” Legend says that if you stick your thumb in the little hole and rotate it just right, you get a miracle. Rumor has it, even Emperor Justinian tried it for headaches—indeed, who needs aspirin when you have ancient architecture?

Recognized as a UNESCO World Heritage Site, Hagia Sophia continues to reinvent itself. After a stretch as a museum, it has returned to its original mission as a place of worship, while its historical displays now live at the nearby Ibrahim Pasha Palace.

Indeed, one shouldn't miss the opportunity to visit here, because where else can you stand in one spot and admire 1,500 years of spiritual remixing? Hagia Sophia’s layers of faith, art, and genius design make it impossible to look away—so go ahead and stare in awe!