The Ghost on the Stairs

At my favourite post-Wednesday walk café, there is a staircase that goes nowhere (shades of the Winchester House in San Jose, California!). When I blipped it today, something must just have passed that way, for there are distinct remnants of ectoplasm floating around, only visible in the photo.
Nothing to do with the spooky coffee at the same café (here) I'm sure. Or is it?