Möbius strips are weird and wonderful mathematical shapes which can be created using paper, crochet or knitting. Marvel at their strange one-sided nature, try to cut them in half, and experiment with what happens with different numbers of twists. Whatever you do, the Möbius strip will surprise you at every turn.
And if a single Möbius strip is not enough for your curiosity, try attaching two together to make these amazing Möbius hearts, as demonstrated by Matt Parker.