You need to finish the Agacion quest 1st.
The npc that gives it is Hamon , in draco.
After finishing the quest , go to "Lorca" in Requeis , get the "re-entering to altar quest" and head to the agacion spot. Exit and you'll get 75k EXP.
You can do it forever , specially if you have telehack it'll take you 10 sec / 75k exp lol.