Sacred Forest Meadow
From Zelda Legends Wiki
It's pretty difficult to get into the meadow, because of the Lost Woods near it. That's why it's called "Sacred". At the time when Adult Link is going to the meadow, Mido is blocking the path. If Link plays the Saria's Song, he let's Link pass.
After Ganondorf's "transformation" to the King of Evil, the moblins found the meadow and began to guard the place.