Last weekend, I read The Witch's Guide to the Paranormal by J. Allen Cross. One interesting concept that it talked about, which I hadn't heard of before, was the idea of a "spirit highway."
Parts of the concept were familiar, like the connection between spirits and running water, but the stories have always been more nebulous: running water often forms a boundary between worlds, that sort of thing.
But the book, which is focused on how to handle household hauntings, takes a more practical approach, talking about how running water creates an energy current and spirits use it as a highway. In particular, if water runs beneath the home, that could cause a haunting.
The book describes the "spirit highway" as a type of portal that creates a corridor through a home or building:
This is a current of energy that spirits can use for faster or easier transportation. I always describe it as something akin to those conveyor belts in the floors of airports that you can step on to either carry you or speed you up when you are in a hurry. These highways can be created by all kinds of things, but some of the common culprits include underground water and historical usage of the land. In the case of underground water, energy flows with water, so occasionally underground rivers or streams will create a spirit highway aboveground. Homes with this type of water running below them may receive frequent activity. Alternatively, if a road went through a piece of property for a substantial period of time, the energy still remains long after it is gone, and it may produce a spirit highway. Same goes for areas a railroad used to run through.
I was particularly charmed by the idea of a sort of "ghost" of demolished road or railway, that hangs out into the present day and is used as transportation for spirits.
That being said, I'm pretty curious how often a road is destroyed and a house is built on top of its old path. Maybe it's just because I live in New York City, a location whose highways famously destroyed entire communities, but it's hard for me to imagine roads making way for houses and not the other way around. (Highways often feel like an awful genie that we can't quite put back into the bottle.)
However, the running water detail felt particularly relevant to life here in NYC. Like (I assume) many other cities, many of our creeks and streams have been buried so that the land above them could be developed. (There's even a blog and a book dedicated to that history.)
Of course, that's caused environmental issues. Lately, there've been plans to daylight certain creeks in the city to reduce sewer overflow, but it's easy to forget everything that's going on underground—both in terms of lost streams and infrastructure.
While (to my knowledge) I don't live on top of a hidden creek, the massive NYC sewer system is its own network of buried rivers. (The city has 7,400 miles of sewer pipes.)
My general feeling is that New York City is jam-packed with hauntings just because of the sheer population density over hundreds of years. On the podcast, I've talked about how I think pretty much every street in New York City could be considered its own ley line, in terms of spiritual significance (particularly those streets that are on the location of pre-contact trails—such as Broadway in Manhattan and Fulton Street, Flatbush Avenue, and some of Atlantic Avenue in Brooklyn—because of their particularly long histories.)
So, when thinking about hauntings in densely populated urban areas, it's worth considering whether the invisible infrastructure that moves around refuse, people, and electricity—the sewers, subway lines, and power grid—also serve as corridors for spirits to pass through more easily. Forget ley lines—do you live over a real big sewer?