Karl Drais was actually a forest ranger - with a knack for physics and math. Some of his inventions were further developed by other tinkerers, including his "wagon without horses," which later became a railway handcar. His most significant invention was the forerunner to the modern bicycle, which was called a dandy horse. Today, small children learned to ride bikes on similar pedal-free models.

Frenchman Pierre Michaux added pedals to the dandy horse in 1861 to make what was known as the Michauline. Pierre Lallement further improved the design and patented the term "Lallement vélocipède." The model, however, was not particularly comfortable. The front gears were stiff and the seat was so high that falling could be dangerous.

In 1870, James Starley of Britain achieved the next milestone in the development of two-wheelers: the penny-farthing "Ariel." It proved much faster, due to its proportionately enormous front wheel. However, it wasn't particularly stable and riders needed help to get on the bicycle. Falling could result in serious injuries. Starley later developed the first chain gears.

In 1890, so-called safety bicycles - with chain drives and lower seats - replaced the penny-farthings. With this modern model, the world's most famous cycling event the Tour de France, was launched on July 1, 1903 in Paris. Sixty riders raced from Lyon to Marseille, Toulouse, Bordeaux, Nantes and back to Paris. Frenchman Maurice Garin (pictured center) won the first 2,428-kilometer race.

When it came to making life in the ruins of World War II more bearable, people had to get creative with what they had. There weren't a lot of leisure activities in post-war Germany. Here in Berlin in 1953, young people made a cycling track out of rubble.

A soccer game is taking place on the other side of this wall in Vienna. These spectators used their bicycles as stepping stools to catch a glimpse. This historic scene has been repeated over the years. At an AC/DC concert in Cologne in 2015, the band performed on a fenced-in field, while hundreds of ticketless spectators stood on their bikes at the fence to enjoy the show.

Pictured in 1895 are the five sons of Adam Opel. They were all successful racing cyclists and made the Opel bicycles popular. Opel starting producing bicycles in 1886 and became the world's largest manufacturer by the 1920s. The company is now better known for its cars, which it started making in 1899.

To set a world record, tinkerer Frank Dose just had to move his 1,080-kilogram monster of a bike 100 meters with his own strength. He got the idea after a few beers at the heavy metal festival Wacken Open Air. Dose just needed some scrap metal and truck wheels. The most important feature are the tiny wheels at the back - it's not a bike you want to fall over with.

Designer Dieter "Didi" Senft is renowned for his unusual bicycle designs. He has also set several new records with his models. This one, made of elements from 111 garden rakes, is four meters long and two meters high. It is one you can ride too: There's a hip-high seat from which one can sit to push the bike with the feet.

Bicycle collector Ulrich Teige is also specialized in particularly eccentric models. In his museum Pedalwelt (Pedal World), he exhibits exotic bikes like rickshaws, wobbly bikes, reverse-steering bicycles or this one here: a recumbent tandem that only moves when one person pedals forward and the other backwards.

Bamboo bikes are not only stable, they can also be used for long-distance trips. Karina and Tim Poser (photo) traveled with such a model from Hamburg to the Chinese metropolis Chengdu. The bikes, built by a social enterprise based in Ghana and Germany, covered the 12,000-kilometer journey without major problems.

Meanwhile, there are no limits to possible designs. Recumbent bicycles allow the rider to sit in a laid-back reclining position. There are also tall bikes and fat bikes, with oversized tires. This picture shows a cruiser bicycle. These models are particularly comfortable and have an eye-catching design. Their rounded forms and unusual style makes them popular advertising vehicles.

A wooden bar counter, a beer tap, and a sound system: This one-ton vehicle can be pedaled by up to 10 people. The rolling bar has been threatening road traffic safety in German city centers for years. The riders were often way too drunk to properly steer their beer bike: That's why they are now forbidden in most cities.

Here is another example of a particularly creative modification. For the 2008 Summer Olympics in Beijing, this Chinese cyclist added colored wheels to his bicycle to reproduce the Olympic rings.

Beijing long held the title of world capital of bicycles. Autos have since invaded the Chinese metropolis as well. If anyone were to guess the numbers of bikes still cycling through the city, many might be inspired by Katie Melua's hit, the 2005 ballad titled "Nine Million Bicycles."

Several rankings try to determine the world's most bicycle-friendly cities. Ethiopia's capital, Addis Ababa, with its potholes, herds of animals and reckless car drivers, would probably come towards the bottom of such lists. Fearless livestock owners still carry their animals from A to B on a bike. The Danish capital Copenhagen has been elected the most bicycle-friendly city in the world.

Folding bicycles have incredibly evolved over the last decades. They used to be heavy and clunky to ride; new models are easy to fold into a small and easy-to-carry format and can reach normal speeds on the road. They are very popular among commuters, as folding bikes can be carried onto a bus or train at no extra charge, which is not the case with a normal bicycle.

The British folding bike Brompton has reached cult status not only in the UK, but also in Japan and the US. It is the Mercedes of folding bikes: Thanks to its sophisticated gears, it's actually faster than it looks. There are Brompton races held every year in London and New York. At the events, cyclists not only have to be fast, they also compete for the most elegant outfit.

There are different categories of bicycles with electric motors. Some powerful e-bikes barely need to be pedaled, whereas the widespread "pedelecs" simply assist the rider's pedal-power. Although they had a reputation of being the senior citizen's bike, there are now models for all types of extreme cyclists, such as the mountain bikes pictured here. A good bike costs about 2,500 euros in Germany.

A deep declaration of love to the bicycle: While many rent a limousine or a horse carriage for their wedding, this just-married couple picked a bicycle to ride off to their honeymoon. Bicycle weddings are gaining popularity - even among stars: Beyoncé's sister, Solange Knowles, and her fiancé rode to their wedding on white bicycles.