A good at-home half hour cardio workout is stair-stepping. Not running up and down a set of stairs, although that is a good workout. But standing in place with just one stair or elevated platform, and stepping up and down, right foot, left foot, at a good pace. You'll be surprised how much of a workout it is! And of course, as with any workout, you don't abruptly stop but ease off the pace for the last several minutes.