Can someone define the effects of a "physical barrier" that inhibits culture from spreading to another place? Also, could you give an example? I'm having trouble finding anything about it : / ...

Physical barriers are natural things that blocks the pathway to something like mountains, which make it more difficult to pass through.

I'm not sure how to define the effects of a physical barrier but humans have more or less adapted to breaking physical barriers by using airplanes and ships.

But some places could be restricted from whats beyond their homes, like islands that cant see anything but water from the outside or villages that are surrounded by mountains and hills.