The "Barony of Ildhafn" is the name for the Auckland, Waikato and Bay-of-Plenty branch of the SCA, which is an international medieval and renaissance re-enactment group.
"Ild-hafn" means "fire-harbour" in Old Norse (the ancient language of Scandinavia). It's a reference to Rangitoto and Auckland's harbours. Several of the people who founded the Auckland SCA group were passionately interested in Viking or medieval Scandinavian history, so went to those languages for a name.
In 2003 the Auckland and the Waikato SCA groups combined to form a larger group - a "Barony" - which kept the name of the Auckland branch, hence, the "Barony of Ildhafn".
The Waikato/Bay of Plenty part of the group is called the "Canton of Cluain". Locals often say "Ildhafn City" when they specifically mean the Auckland SCA group (rather than the whole region).