The Gimghouls...

First things first.
The Gimghouls are the secret society of the University of North Carolina. They're reputed to be the most secret of the old school secret societies. I've studied after them for years and know next to nothing.

Here's what I do:
The Order of Ginghouls was started by 4 students in 1899. If you care, I can tell you who.
Each member has a heraldic shield. They are hung in the atrium of the graduate library, Davis Library.
There may be a fixed number of members, but I doubt it. I imagine, though, there is a maximum number.
They have a castle. Yep, a real stone castle in Chapel Hill. Its official title is Hippol Castle. It was built in the 1925 by a village a Waldensian stonecutters brought in from Valdese, NC (just a few miles from where I grew up). Nobody can get in; there's a custodian on site with a shotgun.
Every Hallowe'en, at midnight, they march from somewhere on campus to the Forest Theater, an outdoor, stone, Greek-style theater on campus. As they process with lit candles, in black robes and masks, they call and respond in some language (possibly made up, though I doubt it). They have a little ceremony, blow out their candles and dash into the woods. Forrest Theater abuts Battle Park which adjoins the castle's property. I assume they dash back to the castle.
The castle is on the highest point in Chapel Hill's municipal limits. It does not appear on any official municipal maps.
On the site of the castle is Dromgoole Rock. It is a large, rectangular rock with a stain that resembles human blood. Legend says it is the blood of Peter Dromgoole, a UNC student in the early 1820s, who was shot to death in the last duel in NC. Dromgoole really existed (I've seen his school records) and disappeared without trace in 1822.
According to rumor, membership is my invitation. If you ever ask to be a member, you cannot be invited.
Nobody knows who they are or what they do.

I followed one four years ago as they ran through Battle park. I followed it for about 3/4 a mile down a path in the heavy woods. She had a considerable lead and when I saw her, she was seated on a cairn. I walked up to her and realized I hadn't really planned this out and had nothing to say. As I started to speak, four other robed people popped out of the woods. Two grabbed my arms.
The girl stood up, looked up and said "Jason Andrew Eckard,* your curosity will do you no good. Stop following us."
Then they all ran away.
I was petrified. My full name appears on nothing but my birth certificate and I have only told one other person what it was. This girl was not that person. I have no idea at all how she possibly could have known that.
I ran back to my dorm and drank heavily.
Since then, they've kind of become a study of mine.
I know no-one else who knows as much about them as I do.

*I actually have five names. The three name version is what I use legally and what I use here.