I live in southern Brittany.

At this time of year the Fest Noz (evening Breton dances) start in earnest but they are just local dances not festivals. Start at 9.00pm and finish between 01.00 and 02.00 am!

Towards the end of October there are a couple of small festivals round here - "Fruits d'Automne" at Peillac 18/19 Oct and Bogue d'Or at Redon 24-26 Oct (Bogue d'Or means the outer shell of the chestnut -not the entrance to the toilet!) Plenty of music and dancing at both of these and local crafts and masses of roasted chestnuts.

But for next May - July... As mentioned, the "InterCeltique" at Lorient - but it is huge (5000+ performers in the parade on the Sunday!) and, although there are many free events, the concerts, etc. are expensive. The Cheiftains are regular performers. The "Festival de Cornouaille" at Quimper is smaller and very much Breton based.

There aren't festivals like English folk festivals as such. In the holiday areas there are "initiations de danse" where they teach Breton dances and fest noz (evening dances) and fest deiz (daytime dances).

There are a number of huge rock festivals - definitely not like folk fstivals!

Whatever you choose you will receive a great welcome in Brittany.
Bonne Chance.

Julian