Elemental Sanctuary

The Elemental Sanctuary is the gateway between the Minish World and Hyrule. The entrance is located within the courtyard of Hyrule Castle, and opens only once every hundred years. Apparently, it is only visible to children, and as such, not many even know of its existence.

In the center of the main room stands a pedestal for infusing the Four Elements into the White Sword to create the Four Sword. A hidden room in the back also contains a set of stained glass windows which tell the story of the Light Force, the Hero of Men and the Picori Blade.

The Elemental Sanctuary appears in The Minish Cap, and the entrance closes by the end of the game. However, the Four Sword Sanctuary, the altar where Vaati is sealed in Four Swords and Four Swords Adventures, looks like the Elemental Sanctuary, and even contains the Four Elements on their pedestals. Hyrule Historia states that they are the same location.