It is at the southeastern seaboard. To get there, you have to get the sea chart at the temple of the ocean king.
follow the goron kid
you have to become a brother to the gorons, then conquer the goron temple, then ask him if you can keep the pure metal. (after you get it and before you leave!!!) :) :) :)
the island of ruin
first your arxeidia
in the courage temple on molida island
the bow is on molida island in the courage temple
you will find it later on whilst in goron island (sorry i forgot the temples name!)
take it to the sun door on molida island
you must lower the water
well you go to the northwestern region of the sea then go to the island nortwesternly located
Buy a cannon on cannon island and blow the rocks up!!!!
It is on the fourth sea chart where there are three parimyds it is gaurded by a cyclone