If it's anything like WOW, then dungeon will be located in a zone like Rift where there is a portal for you to enter. You will need to make group before you enter the dungeon. Once you kill the first boss in a dungeon all group members will have a timer on them (maybe 3 or 12 hours) where they can't enter the dungeon again. This will make you play longer because you can't just farm a dungeon over and over in the same day. Most items in dungeon are BoP. I am just basing this off WOW since O&C is similar. I don't really know what O&C dungeon will be like.