You can't miss the Palacio Postal, a building so opulent you'll hardly believe it's a functioning post office. Step inside and you're immediately greeted by a breathtaking spectacle of gold leaf, intricate ironwork, and magnificent marble staircases under a soaring glass ceiling. It's one of the most stunning architectural gems in the city, blending several grand styles to create a truly palatial feel. You can even buy and send a postcard from this historic spot for a truly unique souvenir.