Mega cities abound in South America. But few of them are as big and beautiful as Buenos Aires, Argentina. Many first-time visitors will express surprise at the city's strong European feel. It's no surprise, really. Millions of Spanish and Italian immigrants settled there through the late 1800s and early 1900s. And during those boom years, when Buenos Aires was the largest and probably the wealthiest city on the continent, the Porteños (that's what folks from B.A. call themselves) built grand edifices in a decidedly Parisian architectural style.Buenos Aires and its 12.5 million inhabitants (lower right), as viewed from space. Buenos Aires sits along the the Río de la Plata. NASA photo.A view of B.A.'s ubiquitous European-style architecture. Photo by Robert Wright.A view of modern B.A.