What Natural Wonders Should We All See In Our Lifetimes?

We live in an amazing world, full of astronomical, geological, and environmental phenomena. What do you recommend we check out in it?

Whether it's a place (perhaps Belize's Great Blue Hole) or an event (perhaps the Aurora Borealis), whether it's something you saw locally or something you had to travel far to catch a glimpse of, we want to know about the most amazing natural wonder that you've seen.

Tell us in the comments (with a picture, please!) what it is, where you found it, and what makes it so worth going to see.

Image: Aurora Borealis, seen in Norway / Frank Olsen.