Does a bicycle work out

Depends on where youre starting from, and how you ride.

Bicycling is a low-load, high-repetition kind of exercise, which usually don't give that much of muscle growth. But if you've been very passive otherwise, expect to see some development in calves, thighs and buttocks.

The more you ride in high-power situations, out of the saddle, pushing hard, the more muscle growth you'll see.

Don't overdo though, as that kind of riding puts a lot of stress on the knees.

For the knees, spinning light-and-fast is a lot better.