Kasuto

Kasuto is the name of two towns in The Adventure of Link, Old Kasuto and the Hidden Town of Kasuto.

Old Kasuto
The original town of Kasuto was attacked and destroyed by monstrous Moas, forcing its people to flee, although one Old Man stayed behind. Upon Link's first arrival to Old Kasuto, the Moas who have taken over the town are invisible to him, and only by possessing the Cross can the young hero see these flying creatures. The Old Man who is left here informs Link that the town is deserted, and that he must look in the woods to the east in order to find the new village of Kasuto. Once Link has obtained all of the eight Magic Containers in the game, the Old Man of Old Kasuto will reward him with his most powerful spell yet, the Thunder Spell.

Hidden Town of Kasuto
The Hidden Town of Kasuto, also known as the New Kasuto, is found in the eastern woods of the area and is revealed upon hitting a patch of grass with the hammer. One of the elderly woman living here approaches Link and, if the young hero has three out of the four Magic Containers, she will invite him insider her house to claim the fourth and last container.

On the second area of the town is a house with its door wide open. The chimney inside the house has an entrance to it, and entering it leads Link to an Old Man who teaches him the Spell. Using this new-found spell at the edge of town causes a temple to rise from the ground which houses the Magical Key.

Theory
It is often noted that Kasuto is the only town name in The Adventure of Link that does not have a similarly named character in Ocarina of Time. Why this is, is unknown as anyone of slight importance could have gotten this name (contrary to what most people think, the names of the places in The Adventure of Link are not solely used for Sages, as Mido also was named after a place in The Adventure of Link).

This, combined with unused data found by hacking the Ocarina of Time game cartridge, has led to speculation that another sage with the name of Kasuto may have at one point been intended for the game. Some also believe that Kaepora Gaebora was Kasuto since Kaepora is a past sage, and Kasuto isn't a sage mentioned in Ocarina of Time.