When the weather is clear, Twin Peaks pops eyeballs - especially around dusk (or sunrise?). When it's cold, wet, windy, and/or foggy, TP is more of a survival adventure challenge :)
Which two peaks are the actual Twin Peaks is hard to say! The main Twin Peaks tourist area (and parking lot) is clearly not a peak, but there are at least 4 actual peaks in the area.
A network of goat trails provides a great way to explore the area by foot.
Nearby Sutro Tower is visually impressive, but otherwise inaccessible to mere humans.
Wikipedia: http://en.wikipedia.org/wiki/Twin_Peaks_(San_Francisco,_California)