Has it to be a event with active gm's? Or can it also be a npc event starts it? If yes that's my idea:
Name of the Event: Gate of Heaven"You can enter this event only once a week with a 8 man Party."
It should get an restriction like the Chest NPC @ Moradon which you can use once a day , so people can't abuse it.
Main event:
You will enter with a 8 Man party from a NPC in Colony Zone at each Race town to the 9 stages of the Hell. The party will start at the 9th stage of the Hell and work his way up to the last stage.
Plot/action:Each stage will have new monsters in it, at the end of each stage there will be a hard boss fight. Every Boss will drop 1 Head of each Boss, for example the first Boss name is: Belial, he will drop "Head of Belial". With this item you can move 1 stage upstairs, till you reach the last Room, where you will fight agains the Devil himself: Lucifer. After you have defeated him , you get the Key to heavens gate. Which will get you into Heaven.
Rewards: Every player who survived to the end and get into the Heaven will be rewarded with 10k NP + an chaos item + A flag of heaven that proves that you survived it.
Or Flegy makes new item for this event

and every player gets like 10knp and 1 item of these Followings:
Heaven Dagger
Heaven Bow
Heaven Sword
Heaven Shield
Heaven Mace
Heaven Staff
Heaven Spear
or 1 Part of Heaven armor, which looks diffrent than valk and hero but gives same def
+5 hp bonus for each part"Rules: You can't use Rezz in the area and teleports, if you die you will get teleportet out like Forgotten Temple.
Note: This event shouldn't be easy like Forgotten temple or other mobs. This event should be very hard , so people will only win it with skill.