What day of the week? Normally it should be doable, but do leave plenty of room on a weekdy since you'd possibly be with rush hour traffic on the return. As you leave the airport, there are some kiosks with info on bus services into the city (when we were there 2 years ago there were 2 bus shuttle companies, in addition to, of course, taxis and rental cars). You'll likely need to take a subway from where the bus leave you to wherever you want to go (warnng: the trains can be crowded, though I felt they were safe). Do look at a guide book in adance and plan what you want to see. Plus, if you can, a map of the subway system. I'd probably stick to the central area and walk to museums and historic places (such as the presidential palace, that was bombed during the coup that put Pinochet into power). Museums are largely closed on Mondays. I don't remember there being much to do in the airport itself. There is a large Holiday Inn just across the street, with a decent restaurant.