Tabata squats is a great lower body workout. This exercise will isolate the quadriceps (thigh muscles) and will definitely work help you work up a sweat along the way.
Depending on your fitness level, you should aim to do 15 to 20 squats per 20 second interval. The goal here is to make sure that you maintain good form. Do not squat below the knee level so that you minimize risk of injury. If you have a Swiss ball, you can place it below your bum to ensure that you do squat below the knee level.