How to reach Evantil, The Vile Oak
Unless you have completed the Portal Attunement quest for Evantil you'll have to take the long route to this zone. First, let's start in the Guild Hall since that has one of the most diverse amount of portal locations. Purchase the Chunk of Argathian Steel and travel to Argath (shown in the picture above).
Once you arrive in Argath you'll want to travel southeast until you reach the location that's circled in blue on my map above. There's a windy stairwell here which you'll want to follow down until you reach the large open area that's displayed on my map below.
Follow my blue line in the map above to reach Beasts' Domain from where you come down the windy staircase. It's only a little bit to the north, down a hallway and through a door.