Fire Mountain

Fire Mountain is a small volcanic island located just south of Dragon Roost Island on the Great Sea.

The island is always spewing out lava and ash from the top of the island, into the sea below. It is said that inside this small island there is a treasure that can help a man lift anything more than twice his own bodyweight. To apprehend the treasure, Link had to use the Ice Arrows to temporarily subdue the intense spewing of magma, then quickly find a way inside the mountain and retrieve the Power Bracelets.

There also seems to be a Big Octo just off shore that seems to be attracted to this island.

Possible origins
It is believed this island was once part of the Death Mountain Range before Hyrule flooded, but the authenticity of this is yet to be confirmed.