Whether it's a simple platform reached by a scrap-wood ladder (thanks, Dad!) or an elaborately designed aerie made with state-of-the-art materials, when you have access to a tree house, you're living the high life. The hefty, 500-page Tree Houses (Skyhorse Publishing, 2013)—which itself could probably be wedged between branches to create a one-person lookout—is filled with stunning examples the world over that make you want to climb up and hang a KEEP OUT sign . . .

Nasu Tea Tree House

By Takashi Kobayashi

. . . Or, in the case of Takashi Kobayashi, a COME ON IN sign. Kobayashi, a former nature documentary producer who taught himself carpentry and design, built his first tree house, now the Hideaway Café, in a cedar in Tokyo's Harajuku district two decades ago. Since then, he's created 119 others (including a wheelchair-accessible version at a medical center and boat- and mushroom-shaped ones at schools) and formed the collective Tree House People to "break down the feeling of separation that exists between humans and nature." Inspired by teahouses, this cozy, light-filled perch serves as an artists' retreat and has a gnomelike door and a (slightly incongruous?) woodburning stove.

UFO

By Bertil Harström/Inredningsgruppen

The UFO is one of six tree houses that have (not quite) landed in the northern Sweden village of Harads since 2010. Inspired by the film The Tree Lover, about three urbanites who reconnect with nature while building a tree house, innkeepers Britta and Kent Lindvall have turned a Lapland forest plot into a showcase for cutting-edge Scandinavian designers and architects. At their Treehotel, each "treeroom" must be built and operate "while hardly affecting the surroundings"—which is certainly true of Bertil Harström's lightweight UFO from an ecological standpoint, but impossible from a visual one. While a stay here is not quite luxurious or cheap (about US$680 a night for two adults and two children), imagine the vacation photos—especially if you visit during the northern lights!

Mirrorcube

By Tham & Videgård Arkitekter

The views of the Mirrorcube, also part of the Treehotel, are so spectacular that it might be hard to go inside to check out the scenery from the six windows of its birch-plywood interior—except when it hits -22°F, when you'll want to be warm and toasty. It has deservedly been nominated for numerous international architecture awards, most recently Italy's 2013 Barbara Cappochin Architecture Prize, whose jury praised it for being "a small project that brilliantly meditates on the relationship between artifice and nature, capable of being playful and poetic at the same time." The mirrored glass is laminated with a transparent ultraviolet film to prevent bird collisions.

HemLoft

By Joel Allen

This beauty in a stand of hemlocks was built in secret with materials found on Craigslist by Joel Allen, a former software engineer who had lost his job and was living in his car. After meeting a "magical looking character" named Old Man John at a garlic festival, Allen says, he realized that he'd "rather be looking through the window of a cool building, than the window of an LCD laptop." A crash course in carpentry, a construction job working on multimillion-dollar homes, and a quest to find extreme places to sleep led to the HemLoft's covert construction by moonlight on government land. Three years of secrecy ended with a feature in Dwell magazine and Allen's opening up the tree house to the hundred or so souls who were able to find it. The book deal–ready story came to a close with a scuttled plan to put the HemLoft's materials back on Craigslist in package form and its eventual sale to a Whistler wilderness adventure company.

Living the High Life

By Blue Forest

U.K. tree house firm Blue Forest, run by Kenyan-born brothers Andy and Simon Payne, offers a brief and interesting crash course in tree house history: Who knew that Caligula held a luncheon in a plane tree? Blue Forest built this backyard castle complete with a kitchen, a bathroom, and a separate children's wing. One can only hope that the rope bridges connecting the fairy-tale towers, the trapdoors, and the zip wire provide enough stimulation, and the kids find little need to turn on the games room's "plasma TV and game console."

Weavers Nest

By Porky Hefer/Animal Farm

For the male weaver bird, nest construction is part of a Bachelorette-esque dating ritual. A thousand blades of grass and twigs are sourced and woven together with all the expertise of a structural engineer. (As John George Wood writes in 1866's Homes Without Hands, "when the edifice and the builder are compared together, the strength of the bird seems inadequate to the management of such materials.") The excellently named Porky Hefer first built his Weavers Nest tree house for a 2009 showcase of South African design called Southern Guild. His "attempt at bio mimicry" has a steel frame and was woven with the invasive Port Jackson willow.

Honey Sphere

By 02 Treehouse

Inspired by Buckminster Fuller's geodesic domes, the Honey Sphere has 210 diamond-shaped panels for tree branches to break on through to the other side and one big Door: its owner, original Doors guitarist Robby Krieger. As Krieger tells all the people in an interview on E!, music "sounds better when you're out here in this tree house because it's all made of wood, you know, the guitar's made of wood, the tree's made out of wood." If you are handy with an Allen wrench, you can get a customized Honey Sphere plan($1,500) for that special tree in your yard.

Bird Apartment

By Nendo

On one side, it's a 78-unit, fly-in high-rise for birds; on the other, an SRO walk-up (via a ladder) for a human. Clever and versatile Japanese design firm Nendo (makers of chocolate "paint" tubes filled with various hues/flavors; a combination lamp-showerhead; and the Book House, with a bookshelf-clad exterior) is behind this many-gabled structure in the Momofuku Ando nature center—founded by the inventor of instant ramen. In a voyeuristic twist, there's a peephole into each of the smaller units so humans can watch the birdly goings-on.