You tap the door where you need to go.(temple of courage)
You use the salvage arm.
You use the sun key on the sun door in the secret underground cave where you got the way to get through the fog on the island where you got the shovel.
you go to molida island.
im pretty sure u use the sun key somewhere in the depths of the ocean kings temple and the ghost key in the lvl with the 4 girls
After you have gotten the sun key, sail to Molida Island and use the key to open the odd door with the sun crest on it (found by digging underground). This leads up to the Temple of Courage.
You Might have remembered in one of the caves Ciela said that something reminded her of that door it was a sun on the door the sun key is the key to that door
take the second passage way and use the sun key to open the door
U touch it
find the sun key
take it to the sun door on molida island
You have to get the sun key from the oceankings temple
I think it was somewhere near a cave you probably know where it is the place where there is a door with a sun symbol on it where the arrow shooting game is