Cerro San Cristóbal is not just the lungs and backyard of Santiago, it's also a great way to orient yourself in the downtown area, from which it is nearly always visible. There are two main entry/exit points for tourists, which are via Pio Nono in Bellavista, and from Pedro de Valdivia in Providencia. Most people take the funicular (which dates from 1925) up from the Pio Nono side, though walking up the road or hiking up the trail called "El Zorro Vidal" is another possibility.
The peak is nearly 3,000 feet high, and has a 72-foot statue of the Virgin of the Immaculate Conception on top. Daily, many people ride, walk, take the funicular or drive up, and the topmost plaza, Tupahue, is where people sit and congregate before walking up the stairs to the Virgin, or on the way back down for a snack or a drink. The typical drink is mote con huesillo, a very sweet peach punch with wheat kernels and dried peaches in it, but you can have a soda, if you prefer, like Chile's old school traditional Sortebe Letelier, with a cherry inside.
In addition to the plaza, there is a zoo, a botanic gardin, a Japanese garden and a number of other attractions on the hill, and it has been heavily landscaped, so many parts of the hill are blooming at different times of the year.
The teleferico (hanging cable cars) are currently out of order, with no fixed date on when they will be up and running again. Many people take the funicular up and walk down (either on the trail, which starts at Plaza México, a little bit below the uppermost plaza, or on the road.