My wife found this Wednesday night ~9pm session after some assertive Googling, and when we walked through the door a man immediately approached us and asked if we knew any songs. I replied that I didn’t but that I had my fiddle, and it turned out he was one of the session players and insisted that I join.
The four players (Neil, Tom, Niall and Mike, on guitar, banjo, accordion and whistle, respectively) were very good musicians and extremely welcoming. As another person mentioned on the website where my wife found the session, there are a large number of tourists here and there is a bit more attention on the players than at other venues. That said, they were nothing if not appreciative. The bar staff were accommodating and allowed a few of us to chat well after closing time.
All in all, if you find yourself in touristy Killarney on a Wednesday night, this may be the only open session, and it’s a good one.