The Pokéwalker for those that are unaware, is a pedometer type device that comes with Pokémon HeartGold/SoulSilver on which you can store a Pokémon on and as you walk around your Pokémon will gain watts. But what’s cooler (probably not the word I’m looking for) is that you can unlock new routes, discover Pokémon and find items as you keeping yourself healthy.
However, according to Bulbapedia, assuming you make 2,000 steps per mile, you will need to walk 1,000 miles to unlock it all. Should you succeed, you’ll be one lean Pokémon trainer. Unless of course you’ve simply strapped your Pokéwalker to someone, or something else.