As  Laguna, choose "Nah,  just my imagination", then walk down the path. At the
next screen, you'll fight some Esthar Soldiers. After this, take the right path
and  climb down  the ladder. Go to the  next screen, and go left here. Near the
rubble,  grab the Old Key (which silly Laguna loses). Now walk two screens left
and  check the middle hatch. After the lever is removed, backtrack to the start
where you fought the mandatory Esthar soldiers, and take the left path.

Climb down the ladder at the end of this screen, and you'll be in a hall. Check
near the rubble on the left to find another Old Key (which is also lost). These
things will later on reward you. Backtrack all the way again so you get to other
side of the hatches (the right side), and check the final hatch too. Now you can
proceed up north at the screen where you found the first Old Key. In the next
screen, go up. 

Here,  you'll find a  detonator, First press the red switch to move one boulder
and open up the left hatch, then press the blue switch to move the other boulder
and  open up the right hatch. Go to the next screen, and walk the stairs to yet
again  the next screen. Here, proceed and touch the boulder on the left to take
care  of yet another Esthar Soldier. Proceed north. In this screen you can save
your  game. Head north to exit the Lunatic Pandora. Depending on how many traps
you set, you'll fight between one and five battles. If you did all the previous,
you'll only fight two Cyborg Esthar Soldiers. The last will use the "Soul Crush"
attack on Kiros and Ward. This is story related, but be sure to heal up Quistis
and Selphie in the real world.