I have never seen a portal in the campaign so I am pretty sure that this requires a Sandbox match. When you conquer a portal you can teleport to its location but you can't return unless you also own that spot. You can't conquer a spot unless you have an adjacent plot of land already claimed. You can use save manipulation to get this achievement. If you own 1 portal you can teleport, reload your save, and repeat. Gl and happy hunting.