Methods on making "out of bounds" areas?

As the title suggests I am wondering how to make out of bounds areas on my map where areas would still be under construction and not able to get to yet though some parts of the map will be open to players.

What are the methods usually used and most convenient? thank you

 

I would just make a big collider(s) where the player can not pass through. Later you could disable/destory the collider when he "unlocked" the part of the map. you could also add cube at the edges of it where the player would walk through with a texture to make it more obviouse where the map ends If you need help with scripting let me know!

 

There was recently a decent thread on this topic.

 

Yup, missed that one - thanks

@MultiSpoone thanks too mate, if I need any help I know where to come then