I'm going on personal experience when I answer this question, LOL! The astral realm tends to look like whatever you want it to look like, unless the Gods want to show you something specific. Some see it as a city, others a great tree. I see it as a huge cloud of stars. Others may see it as a duplicate of this world.
For me it is different every time. Sometimes it is like this world, sometimes it is somewhere completely different.
I suggest that you try astral projecting yourself to see what it looks like for you. I think that that is the best way to know how it really looks.