[Cancuk]

If you're really interested in mountains, I would say just stay in Argentina because of your time contraints. A week in Buenos Aires (maybe a couple of days at the begining, a couple at the end). Spend the rest of your time around Mendoza (wine country) and in the lake district (Bariloche, San Martin de los Andes, and Bariloche). Heaps of hiking around there. Bariloche is good times as well.

I don't know when you're going, but if it's in our winter, you could go to Mar del Plata south of Buenos Aires or Punta del Este in Uruguay for beaches. I personally wouldn' because of your time restraints.