1. Treehotel, Sweden

The Mirrorcube is camouflaged by mirrored walls that reflect their surroundings. The glass is actually treated with infrared that is visible to birds so they won't fly into it.(Photo: Treehotel)

Building a cool backyard treehouse is the ultimate kids' fantasy: Whether it's a multi-story palace a la the Swiss Family Robinson or just a few cobbled-together planks and a rope ladder, a lofted perch among the trees can be a safe haven from annoying siblings or headquarters for a secret club.

But treehouses aren’t just for the kiddy set anymore. These days, designers and architects have found ways to put an amazingly adult spin on a coveted childhood hideaway. From fully functional modern homes hidden in the tree canopy to tiny personalized getaways accessible only by swinging bridge, these modern treehouse homes and hotels will make you rethink what it means to be a grownup.

First up, treehouse hotel chain, in Sweden:

You may only call theTreehotelhome for a weekend, but the unbelievably innovative designs of thetreehousesuites that make up this Swedish hotel and conference destination make our list for sheer creativity. From artsy to futuristic designs, each of the individualtreehousesinvites a very different sort of commune with nature.

You can stay in the the Bird's Nest, a giant cocoon-like hideaway that may leave birds scratching their heads.

The property also has a conference room, a traditional cabin and a sauna, all in various suites among the trees.To book your very owntreehousesuite, visit.com.

2.Hemloft, Whistler, Canada

The Hemloft was built in secret in a Hemlock old growth forest in Washington state. (Photo: Joel Allen)

The story of how the Hemloft came into being is almost as cool as the structure itself: 26-year-old carpenter Joel Allen built the egg-shaped treehouse in secret, on mega-expensive land that wasn’t his, with mostly free materials he found on craigslist. The carpenter and outdoor enthusiast first came up with idea to build a secret shelter in the old-growth Hemlock forest above Whistler Village while living out of his car.

"I was mysteriously compelled to build something cool, something beautiful ... and apparently, I was willing to go to maniacal lengths to make it happen," Allen said on his website.

It took Allen nearly three years to build the structure, which was hidden on some of the same property as expensive vacation homes. Even though Allen never really owned the Hemloft, the cool design garnered the attention of Dwell Magazine and numerous design blogs. With the secret out of the bag, Allen never really got a chance to live in the structure, and he has since dismantled it and sold it on Craigslist as a DIY project.

To read Allen's fascinating story, visit .

3. Wilkinson Residence, Portland, Ore.

The Wilkinson Residence was built to harmonize with nature. (Photo: Cameron Neilson)

Designed by Robert Harvey Oshatz Architecture, this incredible home looks a bit like a cross between a hobbit hole and an alien landing pad. But the house’s unique, curved shape is meant to evoke the flow of music, which is a passion of the owner.

“The wavy ceiling was designed for acoustic reasons, to reflect sound when (the owner) ,” designer Robert Harvey Oshatz told Apartmenttherapy.com.

Built on a steep slope, the main level of the house is amidst the tree canopy, giving it the feeling of a treehouse. Big windows and use of natural wood from the property help to give the feel of a seamless meld between indoors and out.

4.NelsonTreehouseand Supply, Fall City, Washington

The Bear Creek treehouse, which is in the backyard of famed recording studio Bear Creek Studios in Seattle. (Photo: Nelson Treehouse Supply and Design)

Pete Nelson of NelsonTreehouseand Supply has a job that most people would give anything to do: He gets to professionally make childhood dreams a reality. His family business, NelsonTreehouseand Supply, has got the art of awesometreehousesdown to such a science that it earned he and his family their own show on Animal Planet,‘TreehouseMasters.’ The Fall City, Washington company's custom-builttreehousesare so popular that they've been commissioned to build in 26 states and nine countries so far.

Whether it's a family clubhouse with trapdoors, a BBQ pit, kids' playroom and adults'livingroom; a backyard recording studio that has hosted the likes ofSoundgardenand Heart (Bear Creek); or abrewhousein the disguise of a cathedral, Nelson'streehousesare truly spectacular, if you can afford them.

For Nelson, buildingtreehouseswas a passion he developed as a kid — but he doesn't think that having magical backyard retreat should be off-limits for grown-ups.

"I get calls all the time for kids’treehouses. But I think the adults who are placing the calls are hiding the fact that the," he told the New York Times.

5. Gwdy Hw, Wales

Gwdy Hw's futuristic pod shape makes it stand out against the trees. (Photo: Chris Wild)

Gwdy Hw, pronounced Goody Hoo, is a cozy little mountain getaway with a decidedly rustic feel hidden deep in the heart of the Welsh Mountains. The eco-friendly lofted cabin is built on low-impact floating joints that won't damage the trees and comes with a natural hot springs shower, a compost toilet and a wood-burning stove.

But rather than your traditional a-framed treehouse, Gwdy Hoo stands out for its futuristic pod shape and cool combo of a spiral staircase and swinging bridge.

The neat mountain hideaway sleeps four and is available to rent. So if you fancy a vacation amongst the trees, check out the listing at U.K. leasing company .

6. The Quiet Treehouse, London

The Quiet Treehouse by Quiet Mark and John Lewis, designed by Blue Forest. (www.blueforest.com)

The Quiet Treehouse goes far beyond a child's backyard fort. It's a modern, high-tech home designed to bring you closer to nature by living among the trees without all the loud racket of modern life.The Quiet Treehouse was designed by Blue Forest, a company known for hundreds of eco-friendly treehouses around the world. The firm envisioned "a tranquil tree home … designed to evoke the mystery and magic of a natural woodland environment." With help from the quiet sound company Quiet Mark and John Lewis department stores, Blue Forest designed this home with quiet appliances, including a top-notch sound system to block out noise pollution."Its bold contemporary design can be installed independently of a host tree yet still provides the user with the feeling that they are high in the tree tops looking down on the world below," the designers explain.The home was unveiled this month at London's Ideal Home Show. When the show is over, the house will be donated to a children's hospice center in West Sussex, England.You can learn more about how the home works to draw you closer to nature at .

7. Primeval Symbiosis Homes, Denmark

Wójcik says these structures could be built anywhere in the world. (Image: Konrad Wójcik)

As the world's population balloons, more forests are bulldozed to make room for new homes. But what if we didn't have to knock down trees to make way for houses? Finding a way to stop aggressive deforestation is a passion for Denmark architecture and design student Konrad Wójcik.

"We want to be 'close' to nature, and in the same time we are the ones responsible for its devastation," Wójcik says.

That passion led him to design the Primeval Symbiosis, also called the Single Pole House. The tree-shaped home is built on a single, strong pole to sit above the tree line, which allows the home to leverage the sun's power.

"Like trees, they feed from the sun and gather water in order to survive," he explains. The home's self-sufficient construction would use solar power as its main energy source. Bio-waste and an emergency fireplace would also produce energy and heat when needed.

He designed the home to leave no negative impacts on nature, which includes using recyclable, local building materials that could be reused or returned to the earth once the house was vacant.

8. Glass House, Kazakhstan

Tree In the House design. (Image: A. Masow Design Studio)

A. Masow Design Studio's latest creation twists the traditional boundaries of home design and architecture. Instead of building walls to keep nature out, the Tree In the House concept embraces the location's beauty, making nature the focal point of the home.

The house is set in the mountains of Almaty, Kazakhstan, where precipitation during the winter and spring provide plenty of nutrients for the vast forests of fir trees.Designer Almasov Aibek says the idea of building a home around one of those towering trees is meant to provide "more fusion with nature."Embracing natural surroundings is a common theme in the studio's work. See more on the studio's as well as their .

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The exterior of the Costa Rica Tree House Lodge in Punta Uva, Costa Rica, within the Gandoca-Manzanillo Wildlife Refuge. (Costa Rica Tree House Lodge)