for most games you can never reach the edge of a terrain where it just ends. usually theres collision that limits the play area then the terrain is extended far enough beyond that point so as to look like the horizon. this applies for open world games too, look at world of warcraft your surrounded by water (goes to horizon) and your limited how far out you can go via a fatigue meter. now you mention multiple levels, im assuming that your talking about level streaming with this part. for level streaming you would have the level stream in before the player could see the edge, you can also mask things with fog for instance to hide draw distance. or your doing traditional levels (not streamed) you could limit what the player can see beyond the first level via a canyon, tight hall, door, portal etc. you could also build a small portion of the next level and have it viewable but limit how far it can be viewed.
not sure if thats of any help and i didnt quite completely understand what you were asking, but food for thought.