The actor plays a lobster fisherman in the new Neil Jordan film and fell in love with Castletownbere all over again.
Farrell stayed in local bed and breakfasts, hung out with locals in the pubs and even acted alongside many of them - and there wasn't a tourist or a paparazzo in sight.
He recalls, "There is a sense of isolation and a sense of other-worldliness that comes when you get to somewhere like Castletownbere Island in County Cork. It's really off the beaten track, even as far as the further reaches in Ireland go. It's not on the tourist map.
"It was lovely because the town was a set and the town was a character in the film. We were really just welcomed into these people's lives. We were staying in the B&Bs (bed and breakfasts) and they were all in the film. Every single member of the community was in the movie as extras, with speaking roles.
"We just let the people tell their own story as the backdrop and the foreground for the tale that Neil Jordan wrote. I would visit the local pubs and order a Coca Cola. It was lovely being there for a few months; to wake up every morning and go to work on the film. It was magic.
"It's a place that I have a past with because I did my first professional job there about 12 years ago. It was a four-part mini-series for the BBC, called Falling For a Dancer, set in the 1930s. It was a strange little full circle that I got to go back. I remembered some people from the time that I had been there in the '90s. It hasn't changed that much."