WHAT. The “Stairway to Heaven,” Mount Rainier, WA, begins at the base of a fir tree and spirals to 82 feet into the sky. A rainbow-colored suspension bridge stretches 43 feet over the forest floor. It’s the only way to reach the Treehouse Observatory, which provides expansive views of Mount Rainier and the Nisqually Valley. The Cedar Creek Treehouse accommodation is 50 feet up a nearby tree.