Not my house but a few i have done work on have had some spookey secret finds.
One was a place in rural france. The place had been empty for a very long time and a friend of mine bought it. He came back to collect the windows i had made for him and told me he had found hundreds of what appeared to be 1940's childrens shoes neatly laid out in the loft space in one of the barns.
When i asked what he did with them he said we just left them where the are

Another was in Twickenham, the customer had just bought the house and i was fitting out the place with wardrobes and bookshelves but the sizes of the rooms had me baffled. Some where smaller than others but directly above each other so should have been the same.
The lady of the house pointed out a wierd hatch in the kitchen so i poked a tourch in there to see a hidden room about 2ft wide and 10ft long with a chair in it. No way in or out

My guess is a priest hole.......