If Buenos Aires is the Paris of South America, then there has to be an opera house. And Teatro Colón is that opera house. From opera to ballet and free events for the city's citizens, the Colón is an icon in Buenos Aires.
You can admire the facade from the Obelisco and Avenida 9 de Julio but I recommend booking one of their guided tours to see the opulent interior. There are English language tours but they are limited so book in advance. The tour itself takes 45 minutes.
Foodie Tip: Before or after, go to nearby Avenida Corrientes for a slice of pizza like the locals do after a show.
Want to see more? In La Boca, the Colon Fabrica museum features everything from sets to costumes that is created in their basement factory.