What - you don't fancy yourself on top of one of those open-air double-decker buses, cruising through the capital while tourist information blares through your headphones in the language of your choice?
Not to knock the standard city bus tour - it has its place. But if you're a diehard Borges fan or a scholar of Jewish history, you'll want to book a tour with Eternautas, self-described specialists in historical travel. Led by intellectual types with impressive credentials, these specialized tours cater to a learned crowd, revolving around themes from politics and religion to architecture and immigration.
One to try? The Argentinean Labyrinth ('By presenting the topography of a long lasting dilemma, this tour was designed for the understanding of the political, economical, social and cultural keys that explain Argentina´s current situation.') There's a million-dollar question.