I have long been especially fascinated by the intersection of Celtic and Nordic traditions: two strains of the European folk that are closely related, and yet distinct – but which have mutually enriched each other (even as they have sometimes also fought each other!) for millennia.
Here is one example, vocal improvisation on a Celtic folk song, accompanied by the traditional Swedish nyckelharpa:
And interestingly enough, the young woman in question is Polish! So truly a coming-together of three streams of European tradition: Celtic, Nordic, and Slavic. Awesome!