A rigid structure such as a ladder is disclosed having rotating hinges that allow the ladder to fold up and/or be disassembled and assembled. The hinge or hinges can be provided between ladder sections with one ladder section having a male hinge element, and another having a female hinge element. A cam element provided with the female hinge element can be moved between an unlocked position in which the ladder sections can rotate with respect to each other, and a locked position in which the structure is rigid.