Cycling is special IMHO. It can be strenuous exercise like running, or a casual cruise that's even easier than walking. The speed is highly adjustable and easy to get in the sweet spot for that moment. It's not too slow to get bored, and not too fast to miss out on your environment.

Bikes are also a wonderful expression of physics, and the effect of centrifugal force is a key reason why cycling is special. The property of increasing stability with speed is amazing. Leaning not steering is also wonderful. The flow state you can achieve on a bicycle is unreal. Mind, body, and your physical environment in unison.

There's a mechanical beauty as well, that's easy to understand, but with plenty of depth to dig into and enjoy. Wheels and gear ratios are some of humanity's greatest achievements, and you get to pair that with interesting geometry and materials that have a direct impact on your experience. The difference between riding a junker that's not right for your body and a nice/fitted bike, is like the difference between wearing a burlap sack and a tailored suit.

Physical exercise is good, but bikes are much more than just a means to stay fit and produce endorphins. I wish everyone would bike more. Truly one of life's great joys.