La Noche de los Museos happens once a year in Buenos Aires. Bus lines are free. Museums stay open until the wee hours (and they're free, too). It's one of the best nights of the year.
Definitely Go to Montevideo
I was blown away by Montevideo this past November. It has that bohemian, artsy vibe that I love about San Telmo but you feel like you are in a beach town. I’d been through the city a number of times on my way to the beaches further east, but I...