Teleport: Darnassus

Trainer is located at 41,82 - in the temple of the moon

Using Teleport: Darnassus now will teleport you to a pile of dirt (47.4,18.0) with a forbidding view across the sea to a smouldering Teldrassil.

If however, you go and speak with [npc=141489] just to the north (48.0,25.6), marked with a white speech bubble icon on the map and select the text option;

Can you show me what the world was like before the burning of Teldrassil?

You will be phased to the Darkshore before the Burning of Teldrassil event.

Using Teleport: Darnassus now will teleport the player character to the original portal location within the Temple of the Moon in Darnassus.

It will continue to do so even of you log out or even exit the game, until you speak to [npc=141489] and change the phasing to the present day.

This will also change the portal destination of Portal: Darnassus in the same way.

(minor BfA prepatch spoiler below)

After the second quest chain of the War of Thorns prepatch event (8.0), teleports you to Darkshore 47,43. On a sort of random pile of dirt facing right up to a ship.