Hungary’s Springbike is as beautiful on the outside as it is on the inside. My description wouldn’t do it justice so I copied one right out of Wired:
The Stringbike is a cat’s cradle of alien beauty, a vehicle devastating in its mechanical elegance. Mounted on a sinuous white frame (it also comes in black) the Stringbike’s drivetrain is made up of a triangular aluminum swinging arm connected via colorful Dyneema strings to spring-loaded hubs mounted on the rear axle. You pedal it like you’d pedal a regular bike, and the weird shape of the inside of the swinging arm converts your circular pedaling into a horizontal back-and-forth motion. This force is relayed to the rear by the Dyneema strings, which pull on the hubs and rotate the rear axle. There are two identical drivetrains on each side of the bike, offset by 180 degrees so the pedals can provide continuous power. There’s a complete lack of gears, chains and oil stains.
This is for you, Dad!