I was talking to support at my webhost last night and they commented that there's a second version of my site at /www/wp. Later I looked closely and sure enough. The directory wp exists at the same level as wp-content etc. and contains all the files of the site.
None my other sites have this. I have no recollection of having copied everything to that location.
Is there any way that WP might have done that? And if so, why and when?