Summary
Light, which propagate through the universe, enabled us to visualize the properties of space and the scientists already know cosmic optical illusions, which, for instance give birth to ghost images of galaxies. If space has a folded-in topology, light can go round through space several times et give ghost images for each revolution.
So, a true finite universe with a polyhedral shape can be seen by the play of light as an infinite universe, similar to a giant crystal.