Yes, lunges are evil. I once invented an entire song about how much I hate them while I was doing what felt like an infinite number of walking lunges. The thing is, they are really useful.
Lunges work both your quads and glutes. They challenge your balance. They even give you a stretch! You can do them almost anywhere, with or without weights. If you want cardio, too, you can do them as jumps.
Here’s how to do them. Start standing. (Digression: standing in this context, as Lemony Snicket would say, means your feet are hip distance apart and parallel to each other. Your abdominals are engaged. You could connect your ears, shoulders, hip bones, knees, and ankle bones with a straight line—if you weren’t standing still and all—this is what friends are for, among other things.) Take a giant step forward. It is important that the step really is pretty giant to protect your knees. Bend both knees until the front shin is perpendicular to the floor (not any further forward over your foot!) and the back thigh is perpendicular to the floor. Your torso may try to sneak forward; do not let it. You will know you are doing something right if you feel a good pulling sensation in your back thigh. Straighten both knees and return to your initial standing position.
You can continue doing one side until the end of your set, or you can alternate sides. If you need more challenge, you can walk your lunges, add weight, or step back into the lunge position rather than forward.
As always, pay attention to your body. If lunges hurt your knees, don’t do them.