The team at Standing Stone Games is taking an iconic phrase from Tolkien's work and turning it into its own game mechanic in The Lord of the Rings Online. The Delving feature debuts with the upcoming Before the Shadow mini-expansion.
Delvings are a major mechanic coming with the mini-expansion, and the team at Standing Stone Games took to the MMO's blog to explain a bit more in detail what it entails. The inspiration comes from an iconic line about the Dwarves delving "too greedily," and it seems the team is trying to take that ideal and turn it into a mechanic.
As such, players will receive a Delving gem called "Unnerving Zircon," which sets you up to start your journey. At a special location outside of Before the Shadow missions, players will be able to use that gem to effectively enhance the enemies inside the mission space. How it enhances them, whether it just be through stregnth and stat increses, or if we're going to see something along the lines of New World's Expedition Mutators isn't exactly described here. It just states that the gem "unleashes their malice" throughout the Mission, and these "malices" rotate out on a daily basis. Sounds like a rotating mutator system by that description.
The greater the malice unleashed, the better the rewards will be, with players able to potentially earn gear equivalent to Tier 3 raiding gear (without the set bonuses, though), and more. Completing a Delving mission will get you the treasure, a new Delving gem of the next tier, and Delving Writs which are used to trade with mission barterers for rewards.