Fortress of the Dead (taken from http://www.lineage2.com/)
The Fortress of the Dead is located southeast of the Rune Township and is a contested hideout similar to the siege style of the Devastated Castle clan hall. It is of the highest grade among all contested clan halls.

Only a clan level 4 or higher may participate.
Siege registration is open up to two hours before a war and is scheduled through the messenger NPC outside of the clan hall.
The siege war follows the same rules as Devastated Castle. The siege war goes on for one hour, and the clan that contributes the most to killing Lidia von Hellmann takes possession of the clan hall. If the followers of Lidia von Hellmann, Alfred von Hellmann, and Giselle von Hellmann are killed, the clan hall war will be a lot easier.
The siege war ends upon the death of Lidia von Hellmann; just as in Devastated Castle, and if there is no clan that has killed the applicable NPC, the clan hall is under the NPC’s possession until the next siege war.
The clan that owned the clan hall previously will be automatically registered in the next clan hall war.
The possessing clan hall leader can ride on a wyvern.
Devastated Castle (taken from http://www.lineage2.com/
The Devastated Castle is an occupied clan hall that is acquired by siege battle with NPCs. The siege is set up to take place with the NPCs every week, which is different from other sieges. The clan hall battle for the Devastated Castle is always defended by an NPC clan and the ownership to the castle is maintained for one week by the PC clan that is able to defeat the defending NPC clan and take the castle.
Clan that wants to participate in the battle to occupy and acquire the clan hall must register to participate in advance. Participation in the battle to occupy takes place in clan units and only clan leaders having clans of level 4 or above can apply to register. Clans that already own another clan hall cannot register. The clan that had owned the Devastated Castle previously is automatically registered for the siege and the registration for the battle to occupy must be done at least two hours before the start time. Clans that participate in the battle to occupy the Devastated Castle cannot participate in another battle to occupy another clan hall or siege at the same time.
When the time set for the siege starts, the area inside and around the Devastated Castle is designated as the battleground and the players that are already inside the castle are all kicked to the outside. Leader of the clans that are registered in the battle to occupy the castle can build a headquarters.The rules of battle during the battle to occupy the castle are the same as ordinary sieges except for the fact that everyone is on the attacking side and not on the defending side. However, even if the headquarters are destroyed or an unregistered character enters the battlefield and is killed, players are not restarted at the second closest village like in a siege.
A battle to occupy lasts for one hour and the clan recorded as having contributed the most to killing the head NPC of the Devastated Castle becomes the owner of the clan hall. If the leader is killed, the battle to occupy ends immediately. If no clan is able to kill the leader within the time period, the Devastated Castle continues to be occupied by the NPCs until the next battle to occupy.