Welcome to Callan, if I may extend that greeting!
Callan was founded in 1207 by William The Marshal and apparently gets it name from the High King of Ireland, Niall Caille. It is the second largest town in County Kilkenny with a recorded population of 2,678 in 2022.
As for the cache, this, as the name suggests is magnetic so that limits the possible hiding spots. The hint is a spoiler. Please try not to disturb the magnet!! This is temporarily held in place with fishing line!
Congratulations to deathironwolf on being the First To Find a day (albeit the following year) after publication.