Doing the same thing over and over, no matter how many body parts are moving, will become stale, mentally and physically. You will find yourself reaching a plateau.
If you're primarily a runner, add in cycling, yoga, and weight/strength training.
If you're primarily into aerobics or zumba, try adding a spin class and stairs.
If you're doing bootcamp and circuits, get some long distance cardio in.
Embrace change and embrace something new. Your body will thank you for it.