Complete the dungeons associated with each Realmwalker to Diablo 4 Items maximize your XP gain. The Opals stack with other Elixirs, enhancing your XP bonuses significantly.
Starting the Realmwalkers Quest

Speak to Crusader Damond in Zarbinzet to start the Creeping Hatred quest. Defeating Realmwalkers and completing their dungeons not only provides Opals but also contributes to reputation, granting additional XP.
Locate Realmwalkers

Realmwalkers spawn every 15 minutes in random regions, with one special spawn in Nahantu every hour (available to cheap Diablo IV Items Vessel of Hatred owners). Their locations are marked on the map, making them easy to find.