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Outside the gym (besides running): bicycling, stair climbing (actual stairs), swimming (in pool or lake), rowing (boat), paddling (boat). Bicycling (as well as running) can be used to go places. If you work in a multistory building, you can walk up the stairs instead of using the elevator.

Inside the gym: most of the above have gym machines (or facilities like a pool for swimming) to simulate. Rowing and swimming are full body exercises as opposed to just lower body exercise.