Inverness has folk/Scottish/Celtic music every night, depending on your taste.   Macgregor's Bar, The Highlander, Hootenanny's, The Gellions, Market Bar, An Seomar.    Some venues get so busy at nights it becomes a trial to get a seat or get near the bar.   It's often better to find one of the more obscure places..or an off peak time.. as the teenager-twenties bar crowds can be a bit much.   The Celtic music scene is quite vibrant. Macgregor's and Hootenanny's do sessions of sorts.