I moved a bookcase today was surprised when I looked at the wall. There was a 1/2" gap between the wall and the floor (see photos). The bookcase was not heavy, only used to hold kids games. It was against an inside wall. In one direction, the gap extends a few feet into the room and then the wall and the floor meet as they should. In the other direction, the gap meets an outside wall and makes a 90 degree turn, then disappears in a few feet (see photo).
A window sill in that part of the room seems to have a new crack. I noticed a little cold air at the bottom of the window and then noticed a small crack in the windowsill. The crack seems new (see photos).
What should I think about doing next?
P.S. The paint chips in the photos are unrelated. I removed some old cable TV cables before I took the photos.
Update: Plan now is to take up some floorboards and see what we can see.