See this frame gallery?
Those pictures are hanging from boat hardware, with ropes.
A close up:
I saw this and set about finding a way to copy it. You all know how I feel about nautical things, especially polished metal and rope.
This means I’ve done your research for you.
That hardware is called a boat cleat, and is $5 to $34 here.
You can get good rope at Ace Hardware, Home Depot, and online here. I am guessing that the rope has been glued or staple-gunned to the back of those frames. Or both. For glue, I would probably use Fabri-Tac or Magna-Tac, depending on your rope.
I ordered a pair of boat cleats and plan to use them to hang an old ladder I dragged home to use as art, like so — except without the towels.
I’ll show you the finished project when I can find a handyman who has an 18-foot ladder adaptable to stairs. (Anyone? Anyone!?)
Thanks, Pottery Barn, for the cool idea. (And also for the photos, which PB kindly sent to me.)