Tune of Ages

The Tune of Ages is the third, and last, tune that Link learns for the Harp of Ages. Nayru teaches it to you when you rescue her (after the sixth dungeon) from Veran's grip.

The Tune of Ages unlocks the full power of the Harp. It allows Link to freely travel between the past and present ages. When he plays this tune, he immediately reverts to the opposite age, no matter what his location. (However, if he cannot land in that space in the opposite age, he will be sent back.)

P.S. The symbol for this tune is the same symbol on Nayru's Pearl in The Wind Waker.