A band of glass stretches along the top, giving the illusion that the steel roof is floating. The back corner of the cedar structure, where a cantilevered desk looks out at the hillside, is clear from floor to ceiling. And the front wall opens up—via mahogany French doors—allowing for an unrestricted view of the Richard Meier-designed Getty Center across the canyon. "On a clear day you can see all the way to downtown Los Angeles," Kempel says. But be sure to look down, too. As in any tree house, you'll see branches. Kempel cut a hole in the floor to reveal the fallen pine beneath it.