Frozen's effects team made Elsa's magic grow up with her: as a girl, "very child-like and whimsical", simple snowflakes. But art director Michael Giaimo's team "tried all of these magical castles", and none worked. Disney sent a team to an ice hotel in Quebec, but that trip was "to get a feel for how light reflects and refracts off snow and ice". A hotel can't build itself. A snowflake can: "There is no blueprint or genetic code that guides the growth of a snowflake," writes Caltech physicist Kenneth Libbrecht. Its corners "stick out farther into the humid air", grow faster and sprout branches; slow growth fills flat plates. Disney had asked Libbrecht to explain "the process of branching and plating", and "They also replicated the branching and plating concept in the creation of Elsa's ice palace." In effects supervisor Dale Mayeda's words, the palace "magically grows up around her by branching & plating" from the giant flake under her foot. One catch: grown procedurally, her frost "would be too realistic", so hand-drawn art drove it, "snappy rather than linear and procedural." Director Chris Buck's goal for the ice: "base it in reality, and then take it somewhere magical."

The snowflakes and the crystal hall here are our own growth rule, not film footage.

Who do you know that still sings Let It Go?

Sources: Disney's Frozen production notes, "Setting and Visual Look" (2013); Barbara Robertson, "Winter Wonderland", Computer Graphics World, Nov/Dec 2013 (Marlon West, Dale Mayeda, Jennifer Lee); Jim Hill, Jim Hill Media, 9 Oct 2013 (Dale Mayeda, Marlon West, Michael Giaimo); Ian Failes, fxguide, 2 Dec 2013 (Marlon West); Kenneth Libbrecht, SnowCrystals.com (Caltech).
Sounds: our own, made in code (earshot, CC0).