The New World Festival in Randolph Vermont is just one day, but it's a terriffic mix of celtic, french canadian (never sure what the right term is, and I should know, being here in Vermont) cajun, english and more. They get good performers, many local or regional, good dancing, Not much by way of real participatory stuff outside of the dancing. (I'm a native daughter, and may see if I can put in a plug for some better venue for this.) It takes place on the Sunday of Labor Day weekend, oh, and the kids activities, food and beer are not bad either.