This expansion introduces instanced dungeons to the world of Norrath. That means a group of three to six players can get a temporary dungeon of their very own to explore and complete an assigned mission. You have 30 minutes to get to the dungeon and enter it and 90 minutes from the time the first character enters the dungeon to complete your mission there. There are three rewards: experience (points toward the next level for your class), dropped loot and point accumulation toward earned loot. In addition to the single group missions there are raid missions that take up to 36 players. They are said to be very difficult; I've never attempted a LDON raid so I won't discuss those further.