Istanbul has so many world-famous landmarks. They're genuinely amazing. But then you find out how long they took to build, and it completely blows your mind: the Hagia Sophia was built in 5 years (532-537), the Blue Mosque in 7 years (1609-1616), and Rumeli Castle in just 4.5 months (1451). And somehow they still haven't fallen apart. Compared to European building speeds, they basically get everything done instantly here.