Light load level

Hey! Working on a hobby project.

Wanted to create a main menu that you can walk around in. Since you can walk around in it I wanted a nice surrounding, so I created a world around it to try it out. But an entire world will take way too long to load. So my question:
Any good way to create a surrounding where I don’t have to load a big landscape?
A level which is very light to load

Here is a short gifv of what it looks like now from the players perspective:

And here is a pic of the world from up high:

I was thinking about creating a skybox from the map? Is this viable? But I’d also like to get some depth in the background and not sure how to do that