While the above figure appears to be a sequence of nested squares, it actually consists of a single square spiral.
Continuous Line Illusion
See also
Nested Polygon, Polygonal SpiralExplore with Wolfram|Alpha
References
Seckel, A. The Art of Optical Illusions. Carlton Books, p. 29, 2002.Referenced on Wolfram|Alpha
Continuous Line IllusionCite this as:
Weisstein, Eric W. "Continuous Line Illusion." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/ContinuousLineIllusion.html