Here's a 3 meter long shadow-knitted pi scarf made by Anne Bruvold in Tromsø. Shadow knitting creates patterns that are only visible from an angle. Seen straight on, as in the middle picture, the pattern is invisible.
Black on white digits viewed from an angle
The digits are invisible viewed straight on
A portion of the back of the scarf
Lovely! Anne used 3 plus 14 extra digits, which is my favorite length of
pi: 3.14159265358979. Try saying those digits a couple of times, they
nicely roll off your tongue like a poem.