You're driving down Archer Avenue on Chicago's South Side late at night when you spot a young woman walking along the side of the road.

It's cold, but she isn't wearing a coat. In fact, she's wearing a long white party dress that flutters in the night air and almost glows against the pitch black. She shouldn't be out alone this time of night and you can't help wondering what she's doing out here, so you slow your car down as you come up behind her, roll down your passenger side window, and ask her if she needs some help or could use a lift home.

When she turns to look at you her eyes are distant and hollow and her expression is so vacant that it sends a chill down your spine. In fact, the very air around this girl feels cold. Without a word she climbs into the back seat of your car.

You ask her name and you ask her what she's doing out so late at night, but she doesn't answer any of your questions. She just stares out the back window as teh two of you proceed to travel down the road.

After a few minutes she suddenly calls out, "Stop here!"

And before you can ask her another question she leaps out the back door and runs off into the night. Watching her white dress disappear into the darkness and chill, you see her vanish behind the gates of Resurrection Cemetary without even opening them. Just like that, she's gone.

No, you haven't lost your mind. You've just had an encounter with Resurrection Mary, Chicago's most famous ghost.

Resurrection Mary (named for the Chicago cemetary on Archer Avenue that is associated with her sightings) is one of the best-documented ghosts in the United States. Dozens of people have seen her in recent years, including a gentleman who claims to have actually danced with her all evening before going through the traditional scene in the car that ends with Mary disappearing into Resurrection Cemetary. [See video clip at right.]

According to Chicago legend, Resurrection Mary is the ghost of a young Polish girl from the South Side who was attending a dance a dance at the famed O'Henry Ballroom in the 1930's and, becoming angry with her escort, impulsively decided to hitchhike her way home down Archer Avenue, where she was tragically struck and killed by a passing motorist.

Who was the real Resurrection Mary?

Some researchers believe her to be Mary Bregovy, a young Polish woman who died in an auto accident in 1934. Mary Bregovy is indeed buried in Resurrection Cemetary on Archer Avenue, and at least one caretaker reports seeing her ghost wandering the grounds at night. However, Mary Bregovy was not attending a dance at the O'Henry Ballroom before her death, and she was buried in a lilac dress, not a white one. Even so, she is the most frequently mentioned real person associated with the continued hauntings.

Another line of paranormal research names Mary Minkowski as the famous ghost. Mary Minkowski was a young South Side Polish woman who was struck by a car and killed in 1930 on her way to a costume party. That account gets the dress right, the age right, and neighborhood right, but again, Mary Minkowski was nowhere near the O'Henry Ballroom before her tragic death.

Finally, in what may be the most plausible of all the Resurrection Mary associations, the ghost is said to be the spirit of Anna Norkus, a 12-year-ol Southe Side girl who was taken to the O'Henry Ballroom by her father as a present for her 13th birthday. Anna Norkus left the dance early and was struck by a passing car and killed in 1929.

Folklorists discount the Resurrection Mary sightings as just one city's example of the oldest urban legend on record:

The Tale of the Vanishing Hitchhiker.

In this famous urban legend, a night traveller (unually male) encounters a young girl walking along the road alone. He offers the girl a ride and notices that she is very pale and a chill surrounds her body. She asks to be dropped off at her home, which she says she hasn't seen in years. Often, she is wearing a scarf or a sweater, which she accidently leaves behind when the man drops her off.

The next day, the weary traveller returns to the house to give the scarf or sweater back to the girl, only to be told by her father that it belongs to a young woman, his daughter, who died and was buried in it years ago.

The story of the vanishing hitchhiker has been told since Biblical times, with many subtle variations. Sometimes the ghost is actually the spirit of a God, as in an ancient Hawaiian legend in which the Pele, the Volcano god, appears on the side of a road in this same way, disguised as the spirit of a young woman.

In another popular American variant of the legend, the ghost is the traveller--often a truck driver who died years ago in a crash--and the hitchhiker is the living person. The living hitchhiker is dropped off at a diner where he learns that he's just gotten a ride from a famous specter.

In many forms of the story the young girl ghost is dropped off at her parents house; in others, she is dropped off at the cemetary where she was buried. Sometimes the scarf or sweater is found draped over her tombstone; sometimes there is no scarf or sweater included in the legend.

Most major U.S. cities have a vanishing hitchhiker ghost who is part of local folklore and who is considered to be absolutely real. The older the city, the more likely it is to have such a ghost. The vanishing hitchhiker legend is one of the oldest ghost stories on record, and it still delivers a chill every time.

In the case of Resurrection Mary, many people claim to have had legitimate encounters and some of these encounters are very well-investigated and remain unexplained. Is it all just urban legend and myth? Or do some of these cases point to real hauntings?

My own view is that myth and folklore often address real phenomena that occur in abnormal states of mind. For example, travelling alone at night is known to sometomes induce a form of half-sleep called 'hypnogogic trance'. this twilight state of mind has been extensively studied by neuroscientists, and we absolutely know it exists. In such a state, people frequently encounter mysterious others whom researchers then attribute to dream content masquerading as reality.

In truth, researchers don't know what the people in the hypnogogic trance state are encountering: They only know the trance state is a real physiological event. They guess that the beings encountered in this state must not be real because they know of no such beings and can't see them themselves.

How do they know that is so?

Couldn't it be that the beings are very real but can only be seen when in a specific state of mind? I think it's very possible.

Take a look at the video clips here and decide for yourself.

And if you're driving down Archer Avenue late some autumn night and see a girl walking along the side of the road, make sure she remembers to take her sweater with her when you drop her off.

She keeps losing that damn sweater.