Castle in the Air is the tree-house where the the Walker family resides. It is located at the jungle's edge, near both the town and the jungle.
The tree-house does have the look of a castle, with pinnacles and all. But that is not the only reason why Castle in the Air is far from an ordinary tree-house. It has all the facilities and a few luxuries of an average modern house along with a constant supply of electricity.
It is quite unique, and a fine example would be the way people move about in and out of the house. This is accomplished by a strange lift or elevator which is actually a basket hanging from a height by a thick strong rope. So, although the tree-house embodies the things that urban development brings with itself, it has not lost its touch with nature and simple living.
What makes Castle in the Air an amazing place to live in is the peaceful communion one can have with virgin nature.