How to create a portal/teleport.

I have a game where you roll a ball around, avoid obstacles, and collect as many yellow cubes in the given time. How do I create a portal so that if a player goes on to a certain spot, they will be teleported to another area in the same scene? I'm fine with either an invisible portal that the player unknowingly goes in or like an actual oval-shaped portal that the player can see and just go through. All answers are appreciated. Thanks in advance!