Instructions
Visit City Hall. Enter the break room and exit through the kitchen.
Walk toward the lobby until you see the woman at the front desk. Talk to her and enter "boxQ" and the lady will give you the Aquarium Key.
Exit through the main entrance and walk to toward the bowling alley.
Enter the bowling alley through the main door and walk to the desk clerk. Give him the aquarium key by selecting it from the item menu and walking to the counter. He will give you the address book in exchange.