The Portland Underground aka "Shanghai Tunnels" connected many downtown businesses in Portland, Oregon. From the 1850s to the early 1900s, laborers were kidnapped and sold as slaves. During prohibition, drinking went underground into these tunnels.
Here's how this historic site rates on my haunted formula (as it stands in the early stages of creating the formula):
1. The land is marine sediment and volcanic.
2. They are made of stone.
3. There is a train track not far.
4. There is a waterway not far.
5. It is older than 50 years (1850s).
6. There is a history of trauma/death.
It always intrigues me once you go underground in any site. Basements of houses, though murky dark and damp places, often do have more reported activity. I'm reminded of a "Ghost Hunter's" episode in which the TAPS team investigated a house with three generations living in it. They found the focus of activity in the basement with what appeared to be an intelligent haunting of an elderly man who tried to make himself appear to them, played with the ceiling fan and closet door, and made a few fantastic EVPs. I will continue studying the subtle commonalities in haunted places and let you know as my research unfolds.