Most people will say that racing is mostly for humans on foot, racehorses, and vehicles like cars and motorcycles. While those are the most popular choices, you should also look at greyhound racing which is a unique kind of racing.
Greyhound racing is popular around the world but its main market has always been the United Kingdom. In the 20th century, greyhound racing managed to draw more than 70 million people watching every year. That is a considerable amount for this kind of racing because most people know that horse racing is the most popular format.
Betting on the greyhound races was such a popular activity back then people flocked to the UK just to watch and bet on the matches.