Pokémon Diamond and Pearl/Amity Square

At the northeast and northwest ends of Hearthome City there are entrances to Amity Square, the place where you can take a cute Pokémon for a stroll. These Pokémon are Pikachu, Clefairy, Psyduck, Happiny, Buneary, Pachirisu, and Drifloon

It is definitely worth visiting this place, as you will find many valuable items here along the way.

Items
Also, while walking with your Pokémon, it will uncover an item every 200 steps. It is usually a Fashion item for Contests, but it may also be a rare berry.