You need to be on the Quest Striking at the Heart. In the Arboertum after you clicked the Crystal there is a bunch of Skeletons(13) in the water, respawn timer 50 seconds which give around 2k xp in total so thats roughly like 140k xp . The Room has also more mobs if you decide to come with friends. Best Part of this its an highly restricted Quest Area where you dont see much People and if you see them they run by and the skeletons are non aggro but are all porting to one spot once thyre pulled so you can burn them down easily with aoe.
Spot and xp Proof: hecta - Imgur
Edit: ive done this at level 33