Apparently infinite world?

Hello there. I’m currently making a game in which you’re on a field with some trees, which aren’t enough to block your view. The terrain is flat. The actual level where the action takes place and the player can move is not very big, but it’s being a nightmare figuring out how to make the field look good without being expensive in terms of performance, as well as finding a credible excuse for not letting the player get too far. How would you approach these issues?

Thanks in advance

The easiest option would simply be to add a unpassable fence. Add some more terrain and trees behind the fence and boom!

Although this is a rather cheap option…

An invisible wall of sorts? Maybe? Could probably throw something down with an opacity of 0 or 100 depending on how UE4 does it and it would be transparent. Then you could design the rest of the terrain to the way you want it without the characters being able to move into those areas.

Couple of random ideas:
Surround your level with water/lava and make it kill the player if they stay in too long (KillVolume, I think it’s called?).
Have impassable mountains (i.e. the slope is too steep to traverse).
Or if you want the cheap option (which I’m probably going to use in my game) is just put BlockingVolumes around your level. They’re invisible and stop the player from moving through them. You could dress that up with a fence/hedgerow in front of it.