Hiden Senbazuru Orikata, connected cranes

Take a sheet with a 1 × 2 ratio and cut it down the middle into two equal squares, but not all the way. Leave the two squares joined by 2 mm of paper at their corner. Then fold a crane in each square.

Depending on the orientation you choose, you will get two cranes joined at the beak, the tail or the wings.

This is the principle of the Hiden Senbazuru Orikata, "the secret of folding 1000 cranes". It is the oldest known origami book, published in 1797.

Making some of these models is a real challenge! For the models where you see a triangle marked on the squares, you need to place the two marked squares on top of each other and fold a single crane with them. On some models, this lets you make a whole circle of cranes!