A spectacular double helix is found right at the heart of the Chambord castle in the French Loire Valley: masterpiece stairs that were, very likely according to historians, designed by Leonardo Da Vinci. A unique draft has been recovered (top left, previous page), which shows what it is like to think multidimensionnally: a quadruple spiral staircase design, while Chambord actually features only two revolutions! Two more revolutions would have meant an immense height for the ceiling, which is already huge. Other images depict variations.

Previous page – top left: 1; top right: 2; bottom left: 3; bottom right: 4.

References:

1. Top left: Leonardo Da Vinci Ms B, f. 47 r.
2. Top right: a “house car” project, described in “prix étincelle 2013” (creativity contest in partnership with Lycées Clémenceau et Jules Verne (Nantes)) http://prixetincelle2013.wifeo.com/axes-directeurs.php.
3. Bottom left: http://blogs.furman.edu/frn325/files/2014/11/h2-150x150.png.
4. Bottom right: Leonardo da Vinci, Drawing of a staircase Paris, Institut de France Ms B, folio 68v.

An animated contruction modeling can be found at: https://www.youtube.com/watch?v=9aYgn2fhQIU (in French).