This is the 953rd most frequent Icelandic word.
önundarfirði
"Önundarfirði" refers to "Önundarfjörður," a fjord in the Westfjords region of Iceland.
Here, 'Önundarfirði' is used in the dative case to indicate the place where something was seen.
Við sáum margfalda regnboga í Önundarfirði.
We saw multiple rainbows in Önundarfjörður.
In this context, 'Önundarfirði' is again in the dative case, associated with a location.
Á sumrin er mikið líf í Önundarfirði.
In the summer, there is a lot of life in Önundarfjörður.
In this sentence, 'Önundarfirði' identifies a location and is in the dative case, as it follows the preposition 'í' which governs the dative when indicating location.