I know is an old thread, but you never know, someone might be wondering the same thing! I wanted to point out that Valparaiso and Viña del Mar are two cities an hour away from Santiago, very lovely. Valparaiso is very cultural, you can walk around its colorful hills, like Cerro Alegre, take the funiculars or just walk around.
Also near Santigo, you'll find Cajon del Maipo, where you can go horseback riding, rafting, trekking and more.
Now IN Santiago there's a lot to do, wather you want to see historical and cultural places, or eat great food and enjoy nightlife. Here you'll find some itineraries: http://blog.destinalo.com/category/where-to-go/a-stroll-around-santiago/ almost 5 years ago