Cathedral of Eternal Night is a dungeon whose entrance is located in The Broken Shore in the World of Warcraft game. The minimum level for this dungeon is 110+. The dungeon contains 4 bosses. The end boss of Cathedral of Eternal Night is Unknown.
Cathedral of Eternal Night is a progression dungeon. A progression dungeon will allow people who have low gear to gain higher gear without grinding raids whilst everyone else is enjoying the latest raids. The exact location of where the dungeon will be located is not yet known so for the moment, I've located it on the broken shore where the new raid is located.
Its a four boss dungeon that will see players aiming for the Aegis of Aggramar to enable people to get into the Tomb of Sargeras and defeat the Avatar of Sargeras. It is not known whether you need to run this first before going into the raid but i think most people will run this first anyway.