Leg day is the one Everyone tries to skip,
the reason it is so important is, you don't want to have chicken legs and an unbalanced proportion,
Additionally, if you get a nice Bulky upper body, you don't want your legs holding back your day to day life,
Finally, getting any definition in your legs is hard if you don't have rather muscular legs, you will find other places like your arms will show much quicker,
Today, make sure you warm up your knees first with a few sets of leg extensions before you do your working sets,
If the Lunges are to easy, hold some weights in your hands or put a barbell on your back, you want to make sure you are always using a weight that keeps you within the rep range,
Make sure it's not too heavy or too light, and you should always have one rep left in the tank,
