Exactly how does this benefit us?? Since they like to talk in riddles, I have never figured out what the purpose of this whole event even is.
There are some really nice amulets in there that give extra skills. You can enter there and talk to the one npc to check them out. Sry, but I forget his name. He is on the left towards the back once you enter the "atrium" area. There is also level 62 gear there with dreamland stats, but not so worthwhile anymore.
It is simple. Once a day you can do the event inside. Just defeat harder and harder waves of enemies until time runs out or too many people die. The number of allowed deaths is on the lower left(default) and looks like the score indicator in guild castle drill grounds wack-a-mole game. Dont worry, you dont incur any debt from dying in there; it acts just like a st pheniox redemption. Make sure to loot all corpses after each round to proceed. Every couple of rounds(5 I think) is a boss round. Once the time/death counter expires you get ported out to the atrium. Talk to the npc to convert all the stuff picked up to dreamland sigils, then trade those for the amulet.
edit:
It is a up to a six person party.
The amulets have 10 uses.