If you think treehouses are just for children, think again. Some of these treehouse accommodations are fairly primitive, but others border on luxurious. For example, the 5-Day Treehouse Stay near Anchorage, Alaska, is only for those in "excellent physical condition." Meanwhile, every one of the Treehouse Cottages in Eureka Springs, Arkansas, includes a private deck, a fireplace, and a Jacuzzi bath.