An impossible figure that locally (but only locally!) looks like a torus.
Impossible Torus
See also
Ambihelical Hexnut, Impossible Figure, TorusThis entry contributed by Margherita Barile
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Cite this as:
Weisstein, Eric W., with contributions by Margherita Barile. "Impossible Torus." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/ImpossibleTorus.html