BS The Legend of Zelda: Inishie no Sekiban/Week 4/Overworld part 2

Now warp to the Forest (#4) and go to the Master Sword grotto. Draw the sacred blade from its resting place. You can now use sword magic when at full health, rather than at points determined by the timer.

Anyway, leave the grotto, and take the path to the right out of the Forest. Then head into the Death Mountain Path tunnel.