As far as I know for each race there are currently 2 instances!
The first one you can do between level 30-40 and the second at 35-45. They usually need a little pre quest (access key). You also have some small quests there. At the moment I am farming the first instance (Elyos side) with random parties - you can get best equip for your level there. However the yellow weapons are really rare... so I still haven't got it yet
- you really need to be very lucky. But other stuff as necklaces, earrings, rings, armor etc. shouldnt't take you too long....
The instance itself is not as complex as e.g. Gnomeregan in WoW, I would say its more of the "Palisade", "Monastary" type. You walk through a dungeon with some different named bosses in. I don't know anything about the 2nd instance yet except it is some kind of evil laboratory (with all kind of experimential monsters), but I'll try it out soon
Kind regards,
LD