In the world of Final Fantasy VII, there are four caves scattered across the world containing extremely powerful and useful materia. These caves cannot be accessed easily, but here is a guide on the materia that is contained in the caves, the way in which to get to them, and where the caves are located.

Materia Cave One
Materia Contained: Knights Of The Round
Means Of Transport: Gold Chocobo
Location: A cave on an island on the northeasternmost corner of the world map

Materia Cave Two
Materia Contained: Quadra Magic
Means Of Transport: Airship and a Blue Chocobo
Location: A cave on an isle southwest from the town of Wutai

Materia Cave Three
Materia Contained: HP<-->MP
Means Of Transport: Green or Blue Chocobo
Location: In a cave on the sandy ground north of North Corel

Materia Cave Four
Materia Contained: Mime
Means Of Transport: Green Chocobo
Location: In a cave off the shores of southern Wutai

Note: The means of transport needed to get to the caves that are listed above are the MINIMUM requirements. If you have a Black Chocobo, feel free to use it where the Blue and Green Chocobo's are mentioned, and if you have a Gold Chocobo, you can go anywhere, why waste time with any other chocobo or the airship?