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in 2d: take a square and glue the two pairs of opposite sides together. If you do this with one pair you get a cylinder, and then gluing the other pair gets you a torus. No boundary is left.

In 3d: take a solid cube and glue the three pairs of opposite sides together. Maybe a bit difficult to visualize, but the idea is that if you live in the cube and try to exit it on one side then you re-emerge into the cube from the opposing side.

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Would this allow for Escher type spaces?

Escher's most fantastical spaces would be classified as non-Euclidean, whereas the article here stresses that the spaces it describes are strictly Euclidean.

I think they are rather forms of parallel projection (where farther objects aren't smaller, unlike perspective projection) combined with forced perspective, where things look locally connected from a specific angle:

https://en.wikipedia.org/wiki/3D_projection#Limitations_of_p...

s/Euclidean/locally Euclidean/

Yes, though not with a didicosm. (Unless your standards for Escher-esque spaces are low.)

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