Is biking a good workout?

I'm curious, is biking really an effective workout? I've heard that it can be a great way to get your heart rate up and burn calories, but I'm not sure if it's as effective as other forms of exercise. Can you tell me more about the benefits of biking as a workout, and how it compares to other types of exercise? I'm particularly interested in whether it's a good choice for building muscle and improving endurance.