In one of the exhibits there was an inverted likeness of the Mona Lisa created from spools of thread.
If you will recall, I posted images (twice, I think!) of the "Mondrian" likeness behind the front desk of the Hilton in the Fashion District, NYC. This is similar, but with a twist: when the viewer gazes at the image through the lens it is suddenly right-side-up and properly oriented to the original.
Check it out: