Laputa

Laputa is a flying island of Heaven Tail.

Location
It is a flying island about 4.5 miles in diameter, with an adamantine base, which its inhabitants can maneuver in any direction using magnetic levitation. It has the Castle on the Island.

Birth of the Shinseijū Tree
Using seeds from the fruit of Tree of Knowledge Good and Evil it was discovered that by fusing massive amounts of chakra—such as that of a tailed beast—with the seed, would then cause it to activate and grow. The result was a tremendous tree with massive amounts of chakra. This tree is used to spawn the Chakra Fruit after enough energy and life force is unleashed around the world through the tree's roots, but like a regular plant, it needs a suitable atmosphere to survive (such as Earth's). As such, large amounts of energy are required to supply the fruit's growth; the tree essentially sucks the oxygen that the seed was planted on dry. Human civilizations built flying cities, which were later destroyed by an unspecified catastrophe, forcing the survivors to live on the ground while the sole exception Laputa remains in the sky with Tartarus concealed within a powerful thunderstorm that Tailed Beasts may be able to suppress it.