A single square tile, flipped four ways at random, snaps into endless mazes, knots, and rivers. Named for Sébastien Truchet, who in 1704 worked out how much pattern hides inside one humble tile. Roll a new seed, change the grain, watch order fall out of chance.
Why it works: each tile only has to agree with its neighbors at the edge midpoints, so however the tiles land, the lines always connect. Constraint at the boundary, freedom in the middle — and the eye does the rest, reading continuous paths through pure randomness. The same trick underpins generative maps, mazes, and circuit-board art.