If you were to stretch flat all the membranes of an adult [human]'s lungs they would occupy over a thousand square feet [or 93 square metres]; equivalent to the leaf coverage of a fifteen to twenty-year-old oak.from Adventures in Human Being by Gavin Francis (2015)
If all of the capillaries that surround the alveoli were unwound and laid end to end, they would extend for about 992 kilometres (616 miles).
Image: Leonardo da Vinci