Well it's now later and I'm scratching my head as to what it was and how to put it back together again. I notice it has numbers on some of the pieces, so thinking it's an assembly-required something(s). Basically it consists of some sets of long pieces with holes and whole-length slots in them, each set a different length, and some sets of slats attached to cross pieces. The cross pieces do fit into the slots but don't have holes indicating that they were once screwed into through the holes in the slots. See https://imgur.com/a/bTODtM2
So ... anyone have any ideas?
Moved to Building and DIY to allow discussion which is off-topic elsewhere (chas49)