Night is fascinating to me.  Not just from an environmental standpoint, but from a social one as well.  There is something about the way lights interact with your surroundings at night when you photograph it.  As  a recent transplant to Colorado (11 months at this time), I have been spending hours at night from 9pm to 6am, walking the city, learning it and photographing it, while getting harassed by people in uniform, a camera is a dangerous thing apparently.