Rosemary got nothing but good advice. Buenos Aires is a beautiful city. Quite European in its feel as well as architecturally wonderful. Great nightlife, but exercise caution. There is more need because of its political/economic situation and therefore may not be as safe.
Iguazu Falls is a marvel. Outshines even Niagara Falls. The best way to do it is through a tour. (And I'm not a tour fan.) Brazilian side is the best way to see it.
Ziners: owe you a report on our recent Paris trip.
Lidia and Richard in Los Angeles