Instructions
Travel to Kilika, Bikanel or Thunder Plains. Wander around until you encounter a random battle. If a Chocobo is in the party of enemies, select some "Gysahl Greens" on the "Items" list and feed it to the Chocobo. Defeat the remaining enemies to capture the Chocobo. It will be sent to the ranch. Repeat this until you have captured 14 Chocobos.
Return to the Chocobo Ranch and speak to the Chocobos to assess their status. Set free any Chocobos whose max level is under 5. Keep at least four Chocobos who can be raised to level 5 and are "Bold" in naute. Assign these four Chocobos to be "Chocobo Runners" using the Chocobo Management window.
Dispatch your four Runner Chocobos to the Calm Lands. Leave the Ranch and fight seven random battles. Return to the Ranch. Save your game. Talk to Clasko. If Clasko informs you that any of your Chocobos ran away, reload the game you just saved and talk to him again. Repeat this until he informs you that none of your Chocobos ran away. Speak to the four Chocobos that returned from the Calm Lands and raise their levels to Level 2. Repeat this until they are Level 5. Make sure to save after fighting your battles each time and reload if any Chocobos run away. Also, feed your Chocobos to keep their health at full after they return.
Send your first three Runner Chocobos to the Calm Lands and keep the fourth Runner in the reserves. Leave the Ranch and fight seven random battles. Return to the Ranch and save your game. Talk to Clasko. Reload if any Chocobos ran away. Refill your Chocobos' health. Send your second, third and fourth Chocobos to the Calm Lands and keep your first in hand.
Leave and fight seven random battles. Return to the ranch and Clasko will notify you that the Chocobos have found something in the back of the ranch. Head there to find the newly opened entrance to the secret dungeon.