In 2018 I wrote a Qualia Computing article describing how you could create a physical simulation of 3D hyperbolic space you could hold in your hand combining gradient index optics and one way mirrors in a dodecahedron. Here is a simulation of what I have in mind :D What's more, here the dodecahedron's "internal light geometry" smoothly goes from Euclidean to Spherical to Euclidean again to Hyperbolic (all 3D). Left shows what this looks like with one-way mirrors, and the one on the right what it looks with just a transparent plain glass. Notice that in the transparent plain glass Euclidean case the dodecahedron disappears! (because the index of refraction is set to be exactly the same as that of the surrounding medium) Cheers! :-) Original article: qualiacomputing.com/2018/08/…