dangriss wrote:
Find a busy indoor area, such as an airport, theater or bus station, where you can position your camera up high. Use a ND filter for a really long exposure. The people moving around will ghost out and leave even the busiest location looking almost empty.
This was done many years ago by a young woman who wanted to shoot NY subway stations but was concerned about going to some late at night. The portfolio was published in one of the popular photo magazines.