According to Wikipedia, "The bicycle is the most energy efficient means of transport known to man." (!)

I was also interested to note that the bicycle existed for the better part of a century before inflatable tires or rear-wheel drivetrains were introduced, but the castor trick, which puts the axis of the fork on a different line from the center of the wheel (or is it the point of ground contact)--the feature which makes it possible to steer without using the handlebars--was present from the very get-go, in the 1817 prototype of Karl von Drais.

Also learned: that road-paving techniques (viz the macadam) were a subject of some research and practice long before automobiles.