The Diablo 3 Echoing Nightmare event is an endgame activity that throws hordes of demons at the player. It takes on an important role in Season 28 as it's the key to getting the Whisper of Atonement gem for the Altar of Rites.
How to start the Echoing Nightmare in Diablo 3
The Echoing Nightmare event is available to level 70 characters only, but hitting the max level won't be enough. Players need to find a Petrified Scream which is a rare drop from Greater Rifts. Since that's what the majority of endgame activities consist of in Diablo 3, players are bound to come across one sooner or later.
Once players get their hands on one of them, they need to take it to Kanai's Cube and transmute it. This opens up a portal for the Echoing Nightmare event, and from there players just have to enter it.
What are the Echoing Nightmare rewards in Diablo 3?
While many players will be completing this event for the Whisper of Atonement in Season 28, there is still good loot that drops from it. Rewards scale up to wave 150, so it's worth sticking around until the end if possible.
Possible rewards include gems, crafting materials, Blood Shards, and Legendary items. The enemies won't drop loot individually, so everything will be given to the player at the end. Getting further will give more rewards, so try to stay alive as long as possible. Coincidentally, making it to wave 125 will give players the fully upgraded Whisper of Atonement gem they need, so try to shoot for that.
For more Diablo 3 guides, check out Diablo 3: How to get Tome of Set Dungeon Pages on Pro Game Guides.