Cheat: Secret Areas

In Zanarkand, after defeating Yunalescain and getting the Airship, talk to Cid and select the input command. Enter the following codes to find secret locations:

Besaid Ruins to get Auron's Murasame weapon MURASAME
Mushroom Rock Ravine to get Rikku's Godhand weapon GODHAND
Besaid Ruins to get Rikku's Victorius weapon VICTORIOUS
 

Cheat: Secret Airship Areas

Once you get the airship in Zanarkand, use these coordinates to find secret locations:

Mi'hen Ruins X=33-36, Y= 55-60
Battle Site X=39-47, Y=56-60
Omega Ruins X=69-75, Y=33,38
Baaj Temple X=11-16, Y=57-63
Sanubia Sands X=12-16, Y=41-45
Besaid Falls X=29-32, Y= 73-76