Stand in front of the landmine with your feet hip-width apart and your back straight. Grasp the landmine barbell with one hand, holding it at at your side with your palm facing in towards your leg.
Take a step backward with your foot on the same side that you're holding the barbell, lowering your body into a lunge position. Bend both knees to lower your body down until your front thigh is parallel to the ground, or as low as your flexibility allows. Keep your torso upright, your chest lifted, and your core engaged throughout the movement.
Push through the heel of your front foot to return to the starting position. Repeat for desired number of reps before switching sides.