The Legend of Zelda: Majora's Mask/Southern Swamp

As mentioned by Tatl, you need to head to the swamp.

To proceed, you need to head through the swamp area. Bypass the first building, and head to the river in the left; you should see a large cauldron. Head down the pathway behind it (past the Deku babas) and you should see the Magic Hag's potion shop. Bypass this as well, and head into the forest behind the building.

Speak with the monkey, and follow him. He will lead you to another hag that was injured by the skull kid. Talk to her and return to the potion shop to get a Red Health potion (along with a glass bottle). Head back into the forest and give the potion to the injured hag.

Swamp places of interest

 * South of Termina Field is a small path that forks off to a shooting range. You need to bring your own bow.


 * South of Termina Field is a heart container on a dead tree. This tree is climbable, but there is a keese guarding the container at point blank.  If you don't have a ranged weapon, wear the Deku mask to take it out.


 * The swamp building has a deku nearby. Give him the land title for the deku flower in south clock square to gain access to the nearby heart container (and the swamp title deed).  After giving the deed, you can purchase Magic Beans once you know how to use them.