The main item in this dungeon is the slingshot. A map and compass can be found as well.
Queen Gohma, a giant gohma, resides here. She has many minions she will order to attack you, and she will climb on the ceiling and attack you from above. Her weakness is her eye, which you hit with a pellet from your slingshot and then attack her with your sword. It is a good idea to use deku nuts in this battle, because they stun her for a short time, giving you ample time to attack with sword jumps for extra damage.