Some might say that tree houses are just for kids, but the architects of these innovative homes might beg to differ.

1. The glass-enclosed tree

The architect of this house created vertical windows that enclose the tree trunks.

2. Spiral staircase

Flickr: asmith14850

This spiral staircase in Hector, New York winds around a tree trunk.

3. The living room tree

Courtesy of Pazarquitectura

This cement house in Guatemala has a tree growing through the living room.

4. Tree stump house

Courtesy of the University of Washington Libraries Digital Collections

This little house was made from the stump of a cedar tree.

5. The tree-friendly deck

Courtesy of munozarquitectos

This architects of this house in Mexico preserved dozens of trees on the property, including the many trees growing where they wanted to put a pool deck.

6. Beachfront tree house

Courtesy of CoolTreeHouse

The owners of this treehouse on Anna Maria Island in Florida are fighting a zoning battle to keep it.

7. Courtyard tree

Courtesy of Hufft

Even though the house wasn't planned around this small courtyard tree, we like the way a little outdoor space was tucked into the center of the house.

8. Inspired by God

Flickr: Frank Kehren

This house in Tennessee incorporates seven trees. It is currently closed to the public.

9. A-frame house

Courtesy of OnDesign

A house in Tokyo has trees growing though the edge of the roof.

10. The fig tree house

Courtesy of EmailFlyers

The foundation of this 1919 house in Pasadena was built around the roots of a Moreton Bay fig tree thought to be hundreds of years old.

Honorable mention:

Courtesy of The Redwoods Treehouse

It's not a house, but we couldn't resist including this other-worldly pod built around a redwood tree. It's an event venue in New Zealand that holds up to 30 guests.