Origami, or the art of paper folding, finds its roots in Japanese tradition, where it is widely practiced even today. Drawing ...

Trihexaflexagon is constructed by cutting a strip of paper so that it may be marked off in 10 equilateral triangles (A). The strip is folded backward along the line ab and turned over (B).

This is key to solving the numerical puzzles that open the doors themselves. First, interact with the door to "reveal" the puzzle which will show you two triangle patterns that spell out an equation.