In some fitness centers you will find a stairs climber. But an ordinary stairs is just as good, if not better. Because you work against gravity, climbing stairs is more intensive than just walking.
And of course you can make the exercise as intensive as you want. By skipping a step, you can work your buttocks and thighs extra hard. Instead of walking, you can of course also run up stairs if your condition allows it. By walking down at your leisure, you make it an intensive interval workout.