How do I add a teleport location to a map without one?

I know how to add the teleporter npc to the map, but what I need to know is how do I add the teleporter graphic? The actual portal to the map, not just the npc?

The portal the npc stands on with the spinning thing on the top is what I need to add to a map. Is it hard to do?

Example, I want to add one to the doomed maze.