Cactuars on rock in thunder plains

whats the deal with the glowing cactuars on the rocks in the thunder plains??? What are they for??

Press Square to pray to them, and then follow them back to the tower in the south section to receive Kimahri's Celestial Weapon.

The guys in the Thunder Plains are called Quactars for some bizzare reason, but the ones in the desert are called Cactuars. Anyway, only certain stones work when you pray to them, I think you need to pray to 3 of them, then follow the Quactuar ghost, he's REALLY hard to see, just try to look for a bit of Green and you should be OK.

It's a side quest. Not all of the stones work (you can't pray to all of them). Once there are none left to pray to, go down to the beginning and look for the Qactar sprirt that will leade you to Kimahri's Legendary Weapon, the Spirit Lance. Press the ☺ (square) button to have lighting strike the broken lightning tower, use the Celestral Mirror to oepn the chest and get to the weapon. Sweet blood

I've been having a bit of trouble with this one.
Got the Celestial Mirror, and have prayed at 3 stones (I think). The little green guy has appeared, and led me to near a tower on the right hand side of the south screen (near the alcove with a chest & a stone).
But nothing seems to happen. I've pressed SQUARE as often as possible, all around the area, but no lightning strikes the tower.
Any help would be greatly appreciated. Have already completed the Butterfly Quest, and would hate for it to be in vain.

thanks

my memorys a little vague on this when you get led to the big tower you have to run up to it an hit x or square then the weapon is yours :)