When I was a kid (I was probably about 8 or 9) we were on one of usual family holidays on The Isle of Wight.
We had gone to visit Osborne House one day and were walking through the property, following the route through between the red, braided ropes (as you do).
Suddenly my brother (probably about 12 or 13 at that time) piped up that he had found a secret panel!
We looked around at him and he had indeed found a secret panel, however it was only about the size of an A4 sheet of paper, and he was holding it open, putting his hand inside.
Then a gruff voice nearby called out "OY! Leave those light switches alone!".
Clearly, when electric lights were installed, they did not want the switches to be visible, so created a 'nook' to hide them in.