The "walking" meeting
That's my favorite!
This one is more appropriate for one-on-one meeting but works for a larger group too. You just need more organization.
A street/park, fresh air, two people, legs. Not the best one if you have tons of notes to take. But you won't have, anyway.
You'll be outside, breathing fresh air instead of recycled office air, oxygenating your brain. You and your participants will be more energized, more ready to listen, participate, exchange with the others and take decisions. And even without paying attention, you exercice, you build your relationships and it's a great way to resolve conflicts!