The lunge is an oldie but goodie.  Lunges can be a strictly bodyweight movement that can be performed anywhere.

Why do lunges?

Lunges are a great exercise to work the lower part of the body. Lunges can help build stability and strength and improve balance. Depending on lunge variation, they can primarily work the quadriceps, gluteus muscles, hamstrings and calves. Completing lunges can also build core strength as you focus on balance and keeping your torso upright.