Lunges are a workout that I also like to incorporate into my routine with my leg days. It is a test and will leave you sore for awhile if you have never done them before. Lunges work almost every major muscle groups that are found in your legs and it is also a natural move to perform, so it is not a dangerous exercise to perform. The picture below explains how a lunge is supposed to be performed. What I do to intensify this workout is to put dumbbells in both hands and walk around the gym doing them. With the added weight it obviously adds weight to your normal body weight, resulting in building more muscle strength in your legs!