The Monolith of Fate is the main endgame system in Last Epoch. Characters can access the Monolith of Fate from the End of Time, though it is designed to be started after the campaign.
The Monolith of Fate consists of multiple Timelines. All Timelines have a fixed area level and their own set of layouts, enemies and quests to encounter.
Each Timeline contains Quest Echoes, which are milestones in progressing the story of the timeline. In the last (third) Quest Echo you'll encounter the Timeline's boss – killing it guarantees an item from its unique drop pool, and allows you to choose a blessing that provides permanent buff to your character.
Each boss has four unique or set items to offer: two common ones, one scaling with item rarity and a very rare one available only in Empowered timelines.