Favorite thing: I really don't recommend to stay at Antofagasta, not because of the people. Just because this city doesn't have anything interesting to do or to visit. Some people say that make a little tour to "La Portada" maybe could be interesting, but that's all you can do. If Antofagasta is on your route i recommend better to stay in San Pedro de Atacama or wait untill Iquique. But do not stay at Antofagasta and also in Calama that is ugly and also dangerous.
Visit the Vega, an open air farmer's market that is 100% 'legitimate'.
Walk along the coast at sunset, where you see some of the loveliest sunsets ever.