you go to molida island.
You use the salvage arm.
get a salvage arm from eddo and go 2 the place with the sacred crest
get a salvage arm and go get the sun key then go to molida island and dig in front of a palm tree
There is no under water land, but there is the sun key in a box on the sea floor. You have to get the Salvage arm and get the box.
To get the third map you need to get the salvage arm - which you used to get the sun key - and salvage in the top right hand corner of the north western map. That way you can get to south eastern map.
After you visit the temple of the Ocean King for the third time, a spot will be marked on your map That Looks Like a Courage Gem. The Mark is in the middle of the ocean. Go see Eddo and buy a Salvage Arm from him. Go to the spot marked on the map ( The 'Courage Gem' Mark ) and use the Salvage Arm to pull up the chest that contains the sun key.
you go to the green spot and use the salvage arm
When you find the location of the sun key, you will see it's underwater. You can't get that without the Salvage Arm so when you are told to get the sun key, you need to go to Canon Island to get one off Eddo. (Make sure you haven't lost your voice the day you get it. You will need your voice, real loud...)
It's actually shows the area of the sun key. You just fold the ds (close the ds so the top screen touches the bottom). But to get the sun key you need the salvage arm. You'll find the savlage arm on cannon island and you buy it off the man you got the cannon from.
Go to Cannon Island and find a letter for you. It tells you the guy who sold you the cannon has built a Salvage Arm. You can buy it for 200 rupees if you scream loud and long enough. You can try until you get the cheap price. Take the Salvage Arm and use it to search for treasure on the mark on the sea chart. The treasure is the Sun Key. Then head to Molida island go to the first hideaway and use the key on the sun door
To get the salvage arm you need to get where the sun sign tells you to close the ds together and when you start to go to the boat the mailbox will be 'dancing'. See what you got and it will be Eddo and he will tell you that he has finished the salvage arm.
once you are at the part where it says press the symbol to the sea chart click the sun open the sea chart and close your ds/dsi then get the salvage arm (cannon island) go to the courage symbol and salvage