Redwoods are the tallest living trees on the planet. And one of the best places to see them is northern California's Redwood National Forest. They can reach 300 feet high or higher, and their massive trunks can grow to more than 20 feet wide. Recently, a couple of naturalists were searching these woods for tall trees when they spotted something extraordinary.

I said "Michael, get back here, we've got a real tall one." We get our preliminary measurement. And it was so, so amazing, I, I couldn't believe it, you know, it was 4 feet taller than the tallest tree.

They christened the tree "Hyperion" and called in Humboldt State University biologist Steve Sillett to investigate their find. (Yeah, good to know?) Steve is a top redwood researcher with a passion for tall trees.

I think the redwoods are one of the most fascinating species on the Earth. They are at least as fascinating as humans to me.

With the help of the Save-the-Redwoods League and the National Park Service, Steve is studying how a tree can grow this tall and still survive.

I think the big thing that we are really interested in is understanding the biophysical limits to tree height: how tall can they grow?

Steve wants to know the exact height of this tree and measuring from the ground just won't cut it.

The best way to measure tree height is to climb to the top and lower a tape with a weight straight to the ground.

But the best way as usual is also the hardest. Hyperion's lowest branches are 25 stories up. To get to them, Steve uses a powerful crossbow to launch fishing line up and over the tree's branches. Then with the help of wife and climbing partner Marie Antoine, he uses the line to hoist his climbing rope into the tree.

Really it is a big one.

With the rope in place, Steve and Marie walk their way up into the canopy. The climbers move through a high-rise habitat, high above the forest floor. A variety of mosses, lichens and insects make themselves at home in Hyperion's boughs.

So here we are about 300 feet in what may be the world's tallest living tree. And it goes a long way above us, so we are, we still probably are about half hour to an hour from the top. Let's come up to there. Kinda want to put you through here.