SUBREDDIT: r/travel
TITLE: My buddies and I are traveling to Chile in December. Any tips or recommendations?
POST: Hey r/travel, my three best friends and I booked tickets to Santiago, Chile in December. We're going to be in the country for three weeks including during Christmas and New Years.  One of us is fluent in Spanish and the rest are Californians and can get by at an elementary level.

We want to spend at least a few days in Santiago right when we get there.  I understand it's an affluent city, and can get expensive.  As 4 kids just out of college, we are trying to be frugal, but are willing to splurge on once-in-a-lifetime opportunities. 

From what I've heard, most people have found it too difficult or rushed to visit both the Northern and Southern region of Chile and recommend tourists to pick one or the other.  Because of the draw of the Patagonia region, we have tentatively decided on going South.  Should we rent a car to maximize our time and freedom?

Please let us know any recommendations of where, what, and how to see the most important part of Chile.  Also, some tips on what NOT to do.  THANKS!
TL;DR: 
Traveling to Chile in December for 3 weeks with 3 friends.  Need some tips on what not to miss in this beautiful country.