This one isn't particularly hidden, if you consider it's the origin of a name of a fairly well-known town in Bergen County, but then a lot of people have no idea how a given town got its name.
I saw it for the first time when Ivan and I were heading home from an afternoon party. It was dusk, the streetlights were just about to come on, and we were driving down Rock Road in Glen Rock. As we passed the train station and approached Doremus Avenue, I saw it: a big rock in the middle of the intersection.
Well, sort of. It's just off of Rock Road, and Doremus Avenue kind of forks around it, so it doesn't impede the smooth flow of traffic or create a default traffic circle. It's just a very unusual thing to be plopped down in the middle of a largely residential neighborhood. Or maybe the way to look at it is that it's an unusual thing for a largely residential neighborhood to plop itself around.
Indeed, the rock has been a gathering place for a long time. The native Lenape reportedly called the 570-ton boulder Pammackapuka or "rock from heaven" and gathered there for tribal meetings. Upon arriving in the region, early European settlers used the rock as a boundary marker when surveying property. It's believed that the rock was originally transported there by a glacier.
In any case, the Glen Rock rock isn't going anywhere. It seems to be well respected, with a plaque on it to honor war dead. And while it has no protective barriers around it, it seems unscathed by errant traffic. Perhaps the Lenape were right about its source, and some celestial good karma protects it. It's safe to say that if you choose to visit it, the rock will look pretty much the same way it did when Ivan and I stopped by.