Lord of the Rings Online's minigame treasure hunt event should head to The Treasure Field in Ered Luin quickly. The event is now live on all servers but will last only until September 23rd. According to Turbine's latest patch notes for the 7.4 update, there are also new rewards to be found buried deep in the ground.
Players who don't want to take the time to ride out to the field on their own can travel via the special festival announcer NPCs located in West Bree, Michel Delving, Thorin's Hall, and Celondim. More information about the event can be found in the Road to Mordor's treasure hunting guide.