It’s important to remember that Lineage II: Aden is the version of Lineage II that is focused a little more on solo play because the latest event coming to the game today is going to see you grouping up with at least 19 other players (and at most 199 players) to take on Core. It’s the Core Raid Event, you see. You enter the Cruma Tower and then you go on to fight Core. Get in there, defeat Core, and then get all sorts of fun rewards.
What sort of fun rewards? Well, a Core Ring, to start with. (That does seem like the sort of thing you’d expect from Core and not, say, Flag Guardian Greg.) There are also spellbooks and buffs you can received for successfully defeating Core, as well as more special rewards available via the game’s event UI. So if you’re level 76 or above and have a hankering for a new ring and varied rewards, get on in there and fight some Core for them.