How to seamless teleport between two levels?

Can someone help me find a way to seamlessly travel/teleport between two levels?

the issue is the following:
the levels are not allowed to be sublevels of the same persistantlevel,
think of it as teleporting between two persistant levels

why? the reason is simple: im trying to make use of two directlights (one for each level) without them having been overlapped.

Here is a Demo of what im trying to do. (i used skyspheres to simulate the idea)

video one of the demo

video two of the demo

as you can see the portals are rendering whats on the other side.
so i would have to have two levels open at the same time, while rendering a view in one level - from the other level

This sort of thing is in fact done with level streaming.

You can’t have a portal into the second level without one of two things:

  1. The level is already streamed in

  2. The level is actually part of the current level, but hidden ( underneath, for example ).

If you use ‘open level’, everything gets trashed between calls.

I get that you want different lighting in each, but I think you’ll have to fake that somehow. You could have the darker level inside a ball, for instance.

If you really want to keep them separate, then you’ll need to render a video of looking into the second level and play it into the first. I’m sure you can see that’s not ideal, also, if the levels are anything more than almost empty, the transition wont be seamless.

thats what you can see in my both videos. ive already been there.