It actually wasn't a new area; it was a piece of the inside of the structure that had, judging from the stone debris around it, been blown away, at some point, recently, then carefully patched up again with wood and canvas, instead of the stone. Other than that, the structure of the building remains the same, although the pit that once held a nasty ooze has since been sealed up. He'll also sense a single presence in the structure, albeit one that's not alive, yet still moving, in the back, near where the hole was made.