From Ushuaia (on the southern most tip of Argentina) you can choose between two cruises.
The short cruise usually lasts about ten days. This will take you to Antarctica via the famous Drake Passage and you’ll go on many excursions before you head back again. The drawback is that you won’t visit as many places and therefore see fewer kinds of penguins.
Then there’s the long cruise. It takes around twenty days and you’ll also visit the Falkland Islands and South Georgie (made famous by BBC’s Frozen Planet). That means more excursions, more animals and a higher price tag. The choice is yours.