When I was about 10 years old, I spent a lot of time at Fort Frederica National Monument on St. Simons Island, GA. My younger sister and I were enrolled in a summer archaeology camp. We were all having some kind of class at the amphitheater at the edge of the wall by the entrance.
As is typical for me, I was looking all around instead of paying attention to the lesson. Suddenly off to my right, near the center of the fort, I noticed a red shape moving. I realized was a soldier in the traditional black tri-corn hat and British redcoat uniform. He was walking/marching toward the barracks, about half way from the center of town. My sister saw him too. He entered the ruins of the soldier’s barracks, and then never came back out.
The ruins of the barracks are basically some raw tabby walls on the side of a giant field. We would have seen him if he ever left. I don’t remember if we told our teacher, but I’m sure it wouldn’t have mattered if we did. We also would have known if there were reenactors present.
It wasn’t really scary, but we certainly couldn’t explain it at the time. Can’t say I’m any closer to explaining it today!