Portal

A Portal is a magical gateway that usually serves either as a mode of transportation or a means of transformation within the Zelda series. There have been multiple examples of portals seen throughout the series, ranging from the original The Legend of Zelda all the way to Phantom Hourglass, and there have been multiple uses unique to each kind featured throughout the series. They can serve as gateways to other worlds or dimensions as seen in Ocarina of Time and Majora's Mask, as methods of quick transportation as seen in, or as a means of transformation in order to explore new places or things as seen in. The use of portals has steadily grown as the series has progressed, and new uses for them have been known to be developed with each new addition to the series.

Uses
Portals have many uses throughout the series, assisting Link along in his quests against evil by enabling him to meet his needs. At times, he must perform certain tasks to make certain portals available to be used. Typically however there two main uses for portals that have repetitiously been applied throughout the series thus far: transportation and transformation.

Transportation
Of all potential uses to which portals have been put throughout the series, none has been more prevalent than the ability of transportation. Dating all the way back to the original The Legend of Zelda, portals have served as methods of transportation or gateways to permit entry into certain places. This ability has constantly been reused with the development of new games, with portals of varying power and ability acting as methods of quick transportation for Link to places he seeks to reach. They have also been known to be used for transporting Link out of the various dungeons he investigates throughout the series, thus saving the time of having to trek all the way back through the dungeon to reach the exit once the objective has been achieved. Portals have also served as modes of transportation for Link to enter new worlds or dimensions that otherwise would be unreachable by foot or any other mode of transportation for that matter.

Transformation
Another use for portals that has arisen in the series (though largely on only one occasion) has been to transform Link in some manner from his normal form, or in this case his size. This was first exhibited in The Minish Cap, where certain objects found throughout the Overworld turned out to be portals that would allow Link to shrink to the miniscule size of the Minish in order to explore the world the way they were able to. Though they did not really change Link's body in any way in the end, the portals featured at the end of the adult dungeons in Ocarina of Time and each dungeon in Twilight Princess both caused a physical change for Link that included such things as being encased inside a crystal or transforming into Twilight matter in order to be warped out of the dungeon. It remains to be seen whether any new aspects of the end-dungeon portals will be developed for future games, or whether there will be other transformation features.