Neil Jordan's film Breakfast in Pluto was filmed in Callan during August and September of 2005.
But I suppose you are more interested in finding the cache!
As the name suggests, it's magnetic so that makes it a bit easier. If you are at the right location there should be only a few suitable options. You are looking for a small rectangular container.
The hint is a spoiler.
Congratulations to GreenBug and Lulybelle on being joint First to Find a week after the caches were published. For that week at the start of 2025 this area of Kilkenny was deep in snow.