What makes a folk festival sing?

Summer is on the way (or so I hear) and that means, for the Northern Hemisphere at least, a new season of folk festivals. This blooming of musical riches prompts a question: what makes a particular folk festival stand out? What are your favorites? Indoor or outdoor? Multi-day or one long marathon day of folk? Are big names important, or would you rather spend a nostalgic evening with local favorites? “Super Fests” like MerleFest and Bonnaroo seem exciting, yet exhausting, to me. Sometimes, a beautiful star-filled evening with an acoustic melody drifting through the breeze is all I really need. What about you?