It occurs when the player character enters its unique tile, a gated park and opens the resplendent chest inside. Once it is opened the gates will close and Reapers will spawn and attack. Killing all enemies will end the event. Among the loot from the chest is a message from Urzael saying that he has used the Nephalem's greed to lure and trap them in an attempt to kill them. The event can be ignored by simply choosing not to open the chest.