There are four locked cauldrons (KAPPA, CHI, IOTA, and MU) found in the game that have a golden triple triangle symbol above the door, and each one can be unlocked by inputting this combination on the D-Pad: Left, Up, Right, Left, Up, Right.

These are both references to The Legend of Zelda series. The symbol referencing the iconic Triforce seen throughout the series and the other referencing the inputs needed to play Zelda's Lullaby in The Legend of Zelda: Ocarina of Time.

There is another reference that happens when entering your first cauldron of this type. When looting the supply crate inside she says this: "It's dangerous to go alone without supplies. Might as well grab these." This is of course referencing the old man from start of the original The Legend of Zelda who says a similar phrase when giving you the sword.