You could zone into and out of the instance freely and participate in killing anything inside about wow gold once given access. However, once your realm no longer held the highest number of keeps, entry for your realm to DF was cut off and a new realm was allowed in who would inevitably come inside searching for remnants of the previous realm. Inside DF, there were many group and raid bosses, places to farm experience for both leveling, master levels, and artifacts, as well as many players from opposing realms to kill for realm points to get cheap World of Warcraft Gold (equivalent of WoW honor points).

In Aion, the abyss is very similar to that of Darkness Falls. When I first imagined what the "Abyss" in Aion would be, I pictured it to be some medium-sized battleground type area with various floating rocks and crap to fly around on and kinda just do some arranged PvP much like WoW battlegrounds. Boy was I off. The Abyss in Aion is absolutely enormous and the primary threat in the Abyss (at least from what I have seen so far) is not the opposing faction, but rather the NPC faction called the Balaur about wow gold. In the Abyss the Balaur begin with control of pretty much everything except the landing fortresses of the two factions. In order to expand the influence of your faction in the Abyss, raid groups need to siege castles and capture relics under heavy guard by the Balaur Faction.

Almost everything done in the Abyss rewards a player three different ways at the same time: gold, experience, and Abyss points. Thus, doing simple (and eventually very difficult) quests in the Abyss allows you to effectively farm all three things at once and build your standing on the live Abyss rankings to get cheap World of Warcraft Gold.