He's in Biggoron's house.
In Link and the legend of Zelda, Phantom Hourglass, you get the hammer in the isle of ruins, or the island of the dead.
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Molaida Island
On Molida Island.
it is on eddo's island
no its not its on windwaker
On the island of ruins
(it is located at molida island)
on the island
harrow island is in the southeastern sea.
Goron Island! Where else?!
You get it from Eddo on Cannon Island