Immortal Realms: Vampire Wars

very easy just put a lord on the portal, keep using all his action points to go back and forth until it pop's.

the portal spots have to be clamed to use them.

There is a portal in the campaign but I still think Sandbox is the easiest way to get this achievement.

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.