Chicago! The third largest metropolis in the United States, with a population of 2.7 million and a GDP of over $4 trillion, ranking among the top five economies in the world. It boasts the world's busiest airport, O'Hare, and the Chicago Mercantile Exchange, a major hub for steel production, the birthplace of skyscrapers, and is undeniably a world-class first-tier city! #Chicago #USA #urban development #travel recommendations