This is not a huge building by any means but at the time it was constructed in 1936 it was the tallest building in South America. Even today still clearly dominates the views of the area. It is an art deco building with simple lines that never seem to go out of style. I don't believe they provide internal tours.
It is located in an area with plenty of landmarks so, if you don't stay close to it you won't waste valuable time to see just one thing.
Nearby you'll find plaza San Martin, Retiro railway station, The English tower (monumental these days), the modern buildings lines of the Catalinas area and Puerto Madero is only about 12 minutes walk from there.
At the higher end of Plaza San Martin (left) you'll find Florida St which is a famous shopping mall, don't miss the Alvear Palace Hotel right at the beginning of Florida.
On the right (top) of the plaza is the Circulo Militar and several other grand buildings from the golden era of Buenos Aires. Subway line C will take you very close to the area, get off at either San Martin or Retiro Station.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.