Mysterious Walls

Mysterious Walls are inconspicuous, hidden keystones within the caves of The Minish Cap that serve the sole purpose of prolonging the Goron Sidequest. These hidden landmarks are found within the caves of Mount Crenel, Veil Falls, Trilby Highlands, Castor Wilds, and in Lake Hylia, and are activated by fusing blue kinstones with them. Each activated kinstone causes additional Gorons to enter the cave at the far-left corner of Lon Lon Ranch, and help the Gorons already present there to bust down large, rocky walls in their way.

And as the entire goron sidequest is optional, failing to seek out these mysterious walls does not have any effect on the main plot of the game, and one can complete the game just as sufficiently without the aid of the goron sidequest.