The Endless Archive Features Unique Monsters, Loot, and Buffs in Update 40 for The Elder Scrolls Online

mmorpg.com:

Update 40 for The Elder Scrolls Online is coming, bringing the Endless Archive and a series of improvements. The ESO team revealed more about the update, including a deep dive into the Endless Archive dungeon. Update 40 arrives October 30th on PC/Mac and November 14th on console.

The Endless Archive was the centerpiece of the most recent dev stream, and for good reason. 

This dungeon will take you through the halls of Apocrypha. You'll have to face a malevolent Daedra that is threatening to corrupt everything within the archive and the custodian, Master Malkhest, asks for your help to stop it. That's the lore basis for the challenge, and just the beginning.

Since this is a PVE challenge, you'll be able to do it solo or team up with another player or even a companion. When you enter the archive, which you can enter from the map, or if you own the Necrom chapter, you can enter through a physical entrance in Apocrypha. Since this is being added in the base game patch, this is free for all players and will not require any DLC or chapter purchases.

When you enter the archive, you’ll enter your first (of many) stages, where you'll find monsters, dangers, and boss encounters from all over Nirn.You have a limited number of deaths or team wipes if you are teaming up. Battle through enemies and face down bosses for as long as you want (until your final wipe). 

Each stage and each encounter are all randomly generated so you will never have the same experience twice. Three stages and a boss battle will make up a Cycle, and every fifth boss battle you come up against will be against a new monster that is unique to the Endless Archive. This will be considered an Arc. Since this is a new feature, expect a ton of new and unique