Sage Stone

From Zelda Wiki.org

Sage Stones appear in the Earth Temple and Wind Temple dungeons in The Wind Waker. They are large slabs of rock that block doorways, and can only be destroyed with a sage. They have on them the song that must be played to destroy it, the instrument needed to destroy it, and the symbol of the Triforce.

In the Earth Temple, play the Earth God's Lyric with your Wind Waker in front of a sage stone and Medli will follow suit by playing the song on her harp. This will cause it to break. In the Wind Temple, play the Wind God's Aria in front of one of these, and Makar will break it by playing the song on his violin.