Demons - I don't have any personal experiences. But I do trust the word of someone who has. His name is Joe.
I worked with him at TigerDirect (now CompUSA). He was a technician with myself, and we spent much of the time BSing back and forth. One day we got on the topic of Bachelor's Grove and other haunted locations. We decided to take a road trip, where we visited Resurrection, St. James Sag, Maple Lake, and the Grove. He then told me he had something to show me, a "surprise" or sorts.
We jumped in his car and he took me to 108th & 139th, and on the way he told me the story. He has a friend who was/is into the dark arts. And not just dabbling in it, but seriously involved. Joe's friend wanted to take him to "a very evil place" and wanted to know what Joe saw there. Joe, being the type of person that says "I'll do anything once" was up for it, and they went to the intersection. Joe and his friend got out of the car and stood in front of the chain stretching across the path.
This was at night, pitch black, and Joe told me how he had to wait for his eyes to adjust. Joe's friend asked him if he saw anything at the end of the path, and when Joe could make things out, he told me he was silenced with what he saw.
As you can see in the pictures, the trees form almost a tunnel. Joe told me at the end of the tunnel he saw shadows darting back and forth, some small, some big, some huge. There was also a doorway, that seemed to emit what he described as a "dark light". It was darker than the surrounding forest, however it clearly illuminated the shadows moving back and forth. He described them as large-bodied creatures, muscular with long arms and almost a hunched way of walking.
Joe and his friend stood there and watched these creatures, his friend describing to him that this was one of 7 gates to hell in Illinois alone. As his friend was talking, Joe noticed one of the creatures walk across the path, stop, and turn to face them. As the creature began moving down the path, it was growing larger. It was at this point where Joe and his friend decided it was time to go.
Asking around, there was another person who had been there, walking through the forest during the day. He said he noticed a bunch of foundations that were built, but no buildings and no sign of further construction. In one of the foundations this person said he found a brand new tricycle, as if it had just been purchased and placed there.