[Harry Neely] of Dryden, Mich., climbs up to the treehouse he built after he retired. "Treehouses have a little magic about them," he says. Neely's treehouse is fully insulated and heated. The interior is knotty pine, with a ceiling fan and sleeping loft. While many people build treehouses for the kids, Neely built his as a personal retreat. Joanne Neely stands near the sign for her husband's treehouse, "No [girls] allowed."