Invisible walls in games

I know lots of people hate invisible walls as it can break the immersion.

How would you tackle that issue?

My game will just have one forest area that's packed with content to keep the scope reduced, but I'll have NPCs that travel into / outside of that area.

I was thinking about putting a gate that you can't pass (due to some restriction) and others can. But I might also need to block off some areas for the demo and I can't put gates everywhere haha

What did you do, or how would you approach it, or do you not have an issue with invisible walls?