Cave of Chaos Raid

Highly recommended that you have more than 1 res stone and a couple endless potion

10 player party.
Raid Stage consists of 10 room. I heard you'll get 10 more rooms as you cleared myth stage 2 and so on.
Each room will have a total of around 100 monster, approximately you will be dealing with 30-50 monster at once
There will be 3 lottery in this stage; Room 3, 6 and 10.
After clearing the stage, all will receive a box of chaos. Inside could be an accessory, coin box, jewel box or stat stone box.
Accessory received in this stage are better than Lunia Inccarntion but weaker than Lunia Spirit.
Estimate clearing time is around 45min or more.
Experience are around 30mil when cleared.

As for how the stage is, you should try it out yourself. Don't want to spoil your fun

You can also find boxes in those pots thingy lol