This quest can be completed as many times as you like!

Go speak at night to Dionysus Argantma (1015,1010,0), the Centaur Priest, located in the Centaur village, and tell him peace lute.
Following the conversation, he will give you his Peace Lute, which you will need to recharge.

Find 6, 8, 10, 12, or 14 Magical Lutes, dropped by the Morbid Jester in Silversky.

Using the ethereal key, obtained via the Access to the Ethereal Islands Quest, head to the Ethereal Islands.
You need to bring your Magical Lutes to Glaenshenmilandira (1970,2810,0), located in the center of the Ethereal Islands, who will recharge the Peace Lute for you using the keyword peace lute.

Finally, return the recharged Peace Lute to Dionysus Argantma, the Centaur Priest, located in the Centaur village.
He will give you your reward using the keyword peace lute (for this step, you must speak to him at night).

Reward:

• 25,000 XP per level
• 5,000 Gold coins per level
• 1 Celestial Robe (reward not guaranteed)