We have 1 inch plus thick plywood for our subfloors. (We decided to not try to figure out why there was a big hole cut into the floor of the office. Sometimes it just isn't possible to get into the mind of the previous owner.)
With this discovery, we now know why it was so difficult to get the phone line from the basement to the office (post on this to come in the coming weeks), why the house is so quiet and why we do not have a single squeaky floorboard in the entire house.
Here's hoping we make more good discoveries as we continue to Claim Our Space.