I went up onto the roof of the ESO building on a clear evening, and tried a star trail photo. I'd never done one from the city before but I thought it should be possible to do one, with the exposure set so that the buildings were not overexposed but at least some stars showed up. With a 4s exposure at ISO 100, this just about worked. So I took 500 of those and stacked them together, and got some decent trails. There was also someone coming down the trail from Alto del Naranjo to San Carlos de Apoquindo.