In September 2019, Japan House hosted a presentation by SUGIHARA Kokichi, inventor of many optical illusions realised as solid objects. He had brought some examples, and I took pictures (below).
Recently, I have managed to re-create some of his models.
An arrow that always points to the right:
This is what it looks like when viewed from above:
Four blue circles, and four heart shapes, but when seen from the other side (here, through a plain mirror) it's a blue 4-pointed star and the four suits of playing cards:
and this is what they look like from the side:
Six squares, or six circles?
from the side:
A ring of circles, and three concentric circles, but from the other side it's a ring of squares, and three intersecting circles:
seen from the side:
detail of the concentric / intersecting circles from above:
The four suits of playing cards, but the bottom half is made by the reflection of the top half:
Above the mirror, a fish; inside the mirror, its bones:
A flower above the mirror, its flowerpot inside:
There was also a workshop, in which we built this thing:
If you put marbles on the slides, they roll toward the centre, appearing to roll upwards:
This is how the same object looks from the opposite side:
and another side-view:
Marbles, of course, roll downwards:
