I was hoovering at the top of the stairs, first landing, and out of the corner of my eye I spotted someone walking along the corridor (in front of baby elephant) at the bottom of the staircase.  The sighting was very brief, but I did catch sight of the corner and hem of a long patterned dress before the figure disappeared from view.  I went down after the figure but no one was there.  The great hall, however, felt very quiet and calm – not the usual atmosphere at all (to me that is!)