Rarely, I’ve run across a reference to a remodel of an old bank during which contractors are surprised to uncover a vault door that had been hidden by a wall.
Here’s an example where such an obscuring was announced ahead of time, the photo was found on eBay:

Kansas City, MO: 601 Minnesota Avenue, formerly the Commercial National Bank (1925, http://www.emporis.com/building/umbkansasbankbuilding-kansascity-ks-usa) now housing a UMB bank. The newspaper photo and article are dated July 1967, announcing that this York cam-plate door will be encased in a wall in mid-September as part of a massive remodeling (Emporis reports another remodel was completed in 1994). I wonder if anybody realizes the door is there.