[Keyclenef]

The astral can look like the regular world, or it can look like something completely different. The most important characteristic and what makes it 'astral' is the sense you get out of it- usually the astral can deal with concepts and abstractions, with archetypal lessons and/or imagery instead of the same old world you're used to seeing.
For example, I've come out of my body to see my living room and then come out to what looks like woods. Now, at first I can think the woods are the rtz, becasue there's trees, a lake, and people-right? But then you perceive that the atmosphere is somehow 'off'- that the woods and trees are under water, not over it, and that there is a school made of logs in the middle of it, where you go and see something that seems somehow significant- for example you go in and see that the students just graduated and are having a party. I'm describing a place I went to that is the astral. Why do I know that it was the astral? Besides the fact that the regular world doesn't have a log cabin school under water in the woods, there was an element of 'lesson' teaching in it- the cabin was a school, the students were done and leaving, and the natural world (which was beautiful in an 'unreal' way) was being affected by the action of these students. I don't know if this place was created by me in the sense of what it looked like (maybe it would look different to someone else going there) but it was the astral, possibly a teaching temple of sorts. The imagery was archetypal, as in it gave me the sensation of 'making spring' or 'making summer'. Maybe to an ancient greek it would have looked like a bunch of nyadsand dryads frolicking in the trees, because that would be something they would understand, but that's how the 'natural creation or transformation' process looked like me at the time.
I have had other times where I went to a starry field (which is where the world 'astral' is reputed to have come from), and tried to go to the stars, only to find out the 'star' was actually an environment that would look like somewhere in earth or somewhere else (impossible colors, for example) but almost always, when the imagery is 'real world-ish' the content of the environment isn't.
There are places that are completely abstract, that look like one of those cubist paintings that have no defined shape (except for the geometrization of shape) that were beautiful (and almost impossible to describe), and others that are obviously archetypal, like a city in a cave, or underground, obviously inspired by civilizations that believed in the afterlife as either 'underground' or 'in heaven (sky)'. So you see a lot of those.
But first and foremost, the astral is a thought-responsive environment, so you are the one who will give it shape by your upbringing, cultural and familial, and beliefs.
What makes them 'not the RTZ' is that the content of these environments is mostly symbolic and educational.