Originally, this event was only available for a limited time: from dawn on May 15 2015 to dusk on May 21 2015, there was a chance for Herald to the Queen to spawn, which, when killed, would leave an opened portal to the secret level. It can only be opened once per game, and once inside, the entry portal can be used to travel back. The portal stays open for the rest of the game, even after the zone is fully cleared. The zone is always based on the Fields of Misery, but it can be opened from any map on any difficulty level in Adventure mode.