The Frost King's Realm
The Frost King's Realm was the home realm of the version of the Frost King who associated with Madame Tarsa and the Frost King. It was a snowy realm, whose very ground was made of ice underneath the snow, but was nevertheless home to at least one village populated by humanoids, who had their own culture, including the holiday Raenn. The Realm was also home to a caribou-like species, called striberus.
In 2021, CS-NA, Century Smith and Briar found themselves in the Realm was it was invaded by the Mecharons, and managed to defeat them. (PROSE: The Winter Quests)
Behind the scenes
This Realm was a major setting in the earlier The Crew of the Copper-Colored Cupids story, The Frost King's Treasure. It was not actually explicitly referred to as the Frost King's home realm in The Winter Quests, although the dimension's identity would have been clear to any long-time Cupids reader.