Elemental Plane of Air
Imagine being tens of thousands of feet up in the air so high up the ground's out of sight. That's what the Elemental Plane of Air's like: nothing but air. It's a world of brilliant blue, like the sky viewed from the highest mountaintop. It's not featureless, though. Creatures fly through the great vault of endless sky, and other things - chunks of matter from other planes mostly - drift aimlessly about. Winds rise from gentle breezes to raging gales in mere seconds, and then die down as quickly as they came. Most fearsome of all are the storms blown in from other planes - fearsome lightning, giant hail, scorching heat, choking dust, and whirling maelstroms that are ringlike tornados, eating their own tails.
Beings on the plane of Air divide into two classes. There are the natives - djinn and air elementals of all types - who stay to the sky, seldom or never setting foot on the pockets of other stuff that drift by. Then, because the plane's not hostile (and is even beautiful to some), there's a fair number of extraplanar sods here, too, visiting or setting up outposts. Those who ain't natural flyers or elementals from other planes tend to cling to stony, floating islands in the endless sky.
The plane of Air is separated from the Elemental Plane of Water by the Paraelemental Plane of Ice, and from the Elemental Plane of Fire by the Paraelemental Plane of Smoke. Where the plane of Air meets the Positive Energy Plane is the Quasielemental Plane of Lightning, and where it meets the Negative Energy Plane is the Quasielemental Plane of Vacuum.
Note: The Elemental Plane of Air originally appeared in the Planescape AD&D campaign setting from TSR. Its use here is for the purposes of providing context for the campaign only.