I looked thru the Wiki and did a search here but could not find an answer.

I have a small walled city in it's own child-world space (Tamriel is the parent). Everything seems good. now I need a fast travel marker for inside the walled world-space, and a horse marker outside. Best I have been able to figure is that there must be a world location file first, then tag everything to it, but the wiki was vague/incomplete on the subject. I looked at Whiterun and a few other locations but can't figure this out on my own.

How do I add a fast travel marker inside my child-worldspace, that shows up on the game map, and is connected to the parent-worldspace so the horse spawns out there? Thanks for any help.