Treehouses aren't just for kids anymore.
In fact, treehouses are expanding well beyond simple fort-like structures nestled in some branches of a backyard tree: In Costa Rica, there are whole villages of treehouses; in Sweden, you can stay in a different kind of treehouse every night at a Tree Hotel. Tree houses are now tea houses and restaurants around the world.
Click to see 10 of the coolest treehouses in the world.
The Mirrorcube treehouse
This treehouse isn't technically a tree house; it's a tree hotel. But that's not the only way this treehouse, designed by Tham & Videgård Arkitekter, distinguishes itself from others. Thanks to highly-reflective mirrored glass, this 13-foot cube is practically invisible in the woods (a transparent ultraviolent color -- only visible to birds -- is mixed within the glass panes to prevent them from flying into the glass). The rest of the structure is made of lightweight aluminum and plywood, and is accessed through a rope and wood bridge.
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Inside, there's room for two people -- who must pay nearly $700 for the privilege of an overnight stay -- along with a double bed, small bathroom, living room and access to a roof terrace. The Mirrorcube is one of seven different structures in the area, near the small village of Harads, Sweden, close to the Arctic Circle. In fact, they have several other designs, such as ....
...the bird's nest treehouse
The bird's nest treehouse, which relies on four trees for support, looks exactly like its name. Though the outside may seem like a bird-assembled nest, the inside bears resemblance to a modern home, with room for four people among separated living spaces. The 200-square-foot space is accessed through a ladder on the bottom, and rents for more than $650 a night for two adults.
The UFO treehouse
Cast in a lightweight composite material, the UFO treehouse contrasts its surroundings, unlike the bird house and the mirrorcube. The interior, built for five people, has a bathroom and living room and is designed to look spacey and modern. The 300-square-foot space rents for more than $650 a night for two adults.
The Alnwick Garden treehouse
Located in the Alnwick Garden in Northumberland, England, this treehouse is simply too big to be supported by the trees alone, so a network of braces, a concrete foundation, and two concrete towers hidden within the structure support it. However, several mature lime trees stretch through its walls, which are made of cedar, redwood and pine. Walkways and rope bridges lead you off the ground, through the tree canopy, to the treehouse.
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Anyone can visit the treehouse since its completion in 2005, view a film in its education room (called "The Roost"), grab a bite in its restaurant or a drink in its bar, dubbed the Potting Shed, that sits on the treehouse's decks.
4Treehouse, located on Lake Muskoka north of Toronto, Canada, looks like a lantern lit up at night. During the day, its lattice-like skin acts like a tree canopy, filtering and dimming the sun's rays inside the house. The structure was inspired by a hot air balloon frame and hangs on four trees with one steel cable attached to each tree, allowing them to continue growing.
If you look at the Takasugi-an treehouse from the right angle, it doesn't look like a treehouse at all. It bears a much greater resemblance to a bird house, perched atop two thin chestnut trees in Chino, Nagano Prefecture, Japan. Built by architect Terunobu Fujimori, Takasugi-an directly translates to "a teahouse too high" -- and that's exactly why Fujimori built it.
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Fujimori and guests can access the teahouse by climbing a small ladder that leans against the trees. Halfway up, guests must remove their shoes and leave them on a platform before entering the house, which was largely constructed from plaster and bamboo.
The Finca Bellavista treehouse community
Finca Bellavista isn't just one treehouse, it's actually a whole community of treehouses. The community contains 25 structures, including a community center, cafe and five true treehouses. Erica and Matt Hogan founded the 600-acre wild Costa Rican rainforest preserve in 2007 by buying out land that was slated for deforestation.
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Each treehouse takes between a few months and a year to complete and functions as a home, with indoor plumbing and running water and kitchens. The people in the community grow their own food. The residents get around on wooden bridges and a web of zip line cables.
A medieval treehouse
This treehouse is more play place than anything else, but it has the distinction of being located on the grounds of a medieval castle. The grounds of Chateau de Langeais in France feature a castle and garden surrounded by sturdy walls and battlements. Inside the garden is a playground with a tree house, nestled atop the sprawling branches of an ancient cedar.
The free spirit spheres, dubbed Eve, Eryn and Melody, are effectively spherical treehouses, suspended in a grove of trees on Vancouver Island in Canada. Sizes vary: Eve is made of cedar strips and is 9 feet in diameter, with a single bed and a little counter space. Eryn, made of spruce, sleeps two people and has electrical heat, a small fridge and counter space. Melody also sleeps two, has a fiberglass exterior and enough space to work as a studio.
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The spheres are a marriage of treehouse and sailboat technology, the company says. The spheres are built much like a kayak and the suspension points are similar to the chain plate attachments on a sailboat. Stairways hang from the trees as well. The spheres rent for between $155 and $245 each per night.
The minister's treehouse
The nearly 100-foot-tall minister's treehouse in Crossville, Tennessee, is still regarded as the largest in the world. It's supported by an 80-foot-tall white oak tree, but relies on six other oaks for support. It has five stories, each with a wraparound deck, and contains 80 rooms, including a church and bell tower complete with chiming bells.
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Built by Minister Horace Burgess in 1993, the treehouse was open to the public for more than a decade until it was closed in 2012 after the state fire marshal deemed it unsafe. Although a group of local citizens tried to organize a petition to re-open the treehouse, it remains closed today.