Anyone with the right abilities will be able to tell they're energy, illusion, a kind of safe stasis - no one inside is being harmed. If people were to watch, those inside the spaces between will be moved out of them after a time - they're not always there. They're just there for a short period.

If they were to be entered by most people, they would find themselves in another part of the city. Many people go through them. They're also one of the main illusions to hold and are more visible to those with a high level of experience with illusions/trickery magic than just anyone.

They are basically shortcut travel spaces, to fool people into believing the city is bigger than it actually is.