Santi...

I was born in Santiago and I really like it, I can't imagine myself living in another place, but I don't really know it very well. I'll give my best!
If you're in the town and you don't know where to go, you should visit the downtown, there you'll find some important places, like the Goverment Palace called "La Moneda", it is a beautiful white building & you can visit the centerfields too, it's a chilean symbol you can't loose.  If you want to know another historical buildings you can go to Plaza de Armas, it's a tipical square surroundend by the "Catedral", "Correos de Chile" and you can also find some artists painting caricatures and and pretty lanscapes and much more! You should go 'cause it's funny and has a variety of activities to choose.
If you like animals and wild world, "Cerro San Cristóbal" is your place. There you can walk up to the Virgin María, visit the zoo or just lie down on the grass.  If you don't like to walk a lot or you're just tired you always can take the railway or the cable car and take amazing panoramic pictures of the city.  Next to there, it's the "Barrio Bellavista" full of pubs, restaurants and another places you could party in; but if you like to share a drink or coffee or sth else in a peaceful and kinda quiet atmosphere you can go to "Patio Bellavista" where you can find another bussiness and window shopping some craftwork and souvenirs.
Finally if you love Art and all you want is to visit some chilean exhibitions, you have lots of museums, like the "Historia Precolombina" museum, "Historia Natural" museum and "Bellas Artes" museum, there aren't way too expensive and you could spend all day long there. Oh! by the way, you can go there by the subway, it's too easy!
So chose your place and let's have some fun in Santiago!