The Aether is a strange place with few fixed features or inhabitants. It is more of an extra-dimensional space than a proper dimensional world. Historical descriptions of travel through the Aether often refer to sensations of "being drunk while running through a swirling mist of inky blackness".
The Aether can be traveled in a limited fashion through a variety of common magical spells: wink, rope trick, blink, dimension door, passwall, teleport, phase door, shadow walk, vanish, and ethereal presence to name a few. Summoned beings, likewise, travel through the Aether to arrive at their place of summoning. Most wizards use the Aether without ever understanding its nature, or the power that can be gained by mastering movement within it. Most spells and devices use the Aether without allowing conscious movement within its confines - you step into the Aether and you step out instantaneously. As such, movement is restricted and distances rarely exceed several hundred miles.
In his research, Hylax discovered reference to a number of beings who can move within the confines of the Aether. Certainly, high-ranking members of The Family, The Dark Path, and Cult of Shadows use the Aether as a passageway through locked doors. In essence, they step into the shadows, move a few steps, and step out of the shadows. In doing so, they can move hundreds of miles or a few paces into a sealed vault.
There are also reports of spaces existing - albeit temporarily - in the Aether. A large room may exist that in the Realm might be a small, dark alleyway between two adjacent buildings. A notable example of this is Worldswing, the Great Dragon of the Ether, who established - with the help of three powerful artifacts - a semi-permanent castle in the Aether. Ever-shifting, the Aether remain mostly unexplored and completely unmapped.
Hylax's research has also shown that there are creatures which inhabit the Aether - moving through it as easily as humans move through the Realm. It is not clear whether beings from the Realm could survive long in the Aether.
Portals To the Aether
While most spells and magic items allow only simple movement through the ether, more extensive (albeit temporary) use of the Aether can be achieved with powerful artifacts used in conjunction with extensive training or study.
To establish a permanent portal, a vast amount of energy is needed. In order to accomplish this, a chamber must be constructed - a space dedicated to maintain the connection to the Aether. While the location of these permanent portals appear to be random when drawn on a map of the Realm, Hylax's research points to locations coinciding with intersecting lines of force, sometimes referred to as tendrils. He has discovered several "permanent" portals in the Realm. For example, Hylax's encounter with Worldswing in March 832 TA was through a portal at a ruined lighthouse on Thunder and Lightning Point in the Western Reaches. The differences in construction between portals - some are mechanical and others are magical - has led Hylax to hypothesize that several groups of builders might have mastered construction over the ages.