We moved into a historic home in Diamond Hill neighborhood of Lynchburg, VA in 2019
With us were our 2 dogs, one large bouvier with arthritis and the other an active, but older hound dog.
The bouvier couldn't make up the stairs, so he slept downstairs whereas the hound dog followed us up every night to the second floor. Our bedroom was on the western side of the house with several rooms in between the eastern side of the house and a small room that we used as a study. The hound dog, Trooper, would go into every room and location upstairs, about 4 rooms, except the study and the stairs to the attic.
The study was a very small room (6'x10') that is very well lit with 2 large windows, and furniture from our other house (book case, desk, table with tea set and a couple of chairs) and a soft carpet... In other words very nonthreatening. Trooper would not go into the room, no matter how much urging. If I nudged him forward he would whimpered. Sometimes at night I would find him in the middle of the hallway just staring at the open doorway of the room.
Reference the stairs to the attic. The were very wide (5') and well lit by both lights and windows. Trooper would go up a couple of steps, then turn immediately around.
I never knew what Trooper saw... I never heard or saw anything but he was definitely concerned or afraid of those areas of the house. Our 2 cats go into the study all the time and since Trooper passed away we have gotten a new puppy and he doesn't seem concerned about the study, but now that I think about it, I've never seen him go in there either.