Most of all you have to sight city, Santiago is all about its historic center, all the "barrios", there are a lot of great restaurants, and they're very cheap, you have to try the Pisco, there is a restaurant named "como agua para chocolate" it's a lil expensive but it's themed and named after the book, in January they have they annual beer fest. Hope this helps you :) about 6 years ago
If you're into outdoors and nature you can go to Cerro San Cristobal or even Cajon del Maipo (1 hour away from Santiago); or visit parks like Quinta Normal, Forestal or Bicentenario.
If you want to try some sea food, you can go to Mercado Central; typical chilean drinks go to La Piojera and typical chilean food, La Vega Central.
You can visit the museums, take a bike tour to the vinyards or just walk through the Paseo Ahumada.
For anyone looking to go to Santiago, here you'll find itineraries to get you started: http://blog.destinalo.com/category/where-to-go/a-stroll-around-santiago/ about 6 years ago