How the most elite contested clan hall, the Fortress of the Dead, is taken: how to get there, registration, the route through the caster mobs to the last room, and why only the damage dealt to Lidia von Hellmann counts.
Fortress of the Dead is the most elite clan hall that can be captured by a clan, and that clan will use the clan hall until the next siege. The functions are the same as in an ordinary clan hall; I will list them below. It is located in the Forest of the Dead, but that teleport is quite inconvenient: from the teleport point you have to run through the whole location among the mobs, so it is better to use the noblesse teleport to the Cursed Village, only you have to fly there in the daytime, so that there are no aggressive mobs. Though for a clan that has gathered for a clan hall siege that is no hindrance at all.
The siege of the clan hall is held once a week (with us it was Friday, 20:00 Moscow time); you can register for the siege no later than a day before it starts at the NPC Messenger Jacquard, who stands right there at the entrance to the clan hall (there is a nuance here: some write that registration opens two hours before the start, but the last time I checked, I registered without problems several days before the siege).
This clan hall is considered the most elite of all, but its siege is considered the hardest too; I read many forums from the times of the Interlude chronicles on the European official server, and players wrote a great deal there about how hard the clan hall is to capture. Many mobs in this clan hall use magic, and that is why it is rather hard to capture. It is desirable to use mages in the siege too, and preferably with mass spells; it will be easier that way. Half of the mobs run, and they can be gathered into trains by tanks and led to the mages for destruction. But the other half stand in their places and do not want to move at all. It is desirable to hit those from afar, or else they will shower you with hurricanes.
With the start of the siege the whole territory adjoining the clan hall is declared a PvP zone, and monsters appear before the entrance and inside the clan hall. There are very many of them, so everyone needs to know at least a rough plan of action.
The clan splits into two groups: one of the groups will farm the mobs inside the clan hall, the other will defend the entrance from other players. Since you can enter the clan hall only through the gate, the task of the second group is to prevent a mass passage of other clans inside. Separate individuals may break through, but for one person it will be very hard to get through all the mobs, which are simply in crowds and respawn quickly (as far as I remember, the respawn is 3 minutes).
The first group climbs inside the clan hall. We pay no attention to the mobs standing on the sides of the entrance behind the kerbs, they do not reach us (though I once watched a siege on higher chronicles, and there the mobs reach you with nukes), and we break the gate itself (it may seem to you that ordinary mobs stand inside, all the more so as they have the same names as the mobs in the location, but no: these are special mobs without drop and spoil, and their level is higher than that of the ordinary ones).
We go in and run to the left (though there is nothing to run, they stand close by). We remove this whole crowd; the mobs that stood behind the kerb will aggro on you meanwhile, but they still go on standing where they are. We continue moving deep into the clan hall. At the next entrance a new crowd is waiting for us.
We deal with them in the same way as before: those who block the way we bring down, and to the far mobs we pay no attention, they stand still anyway. We turn right round the corner; a few more heaps of mobs are lurking there, already stronger than those met before. Mass spells and mass spells again.
We pass through a narrow little corridor and come out again onto a clearing with mobs, where the wyvern manager stands. That means we are on the right track. From the wyvern manager you have to turn right; there will be an entrance to a room, and that is the last corridor before the throne room (though there is no throne there at all). Again we bring everybody down with mass spells. And at last the throne room.
As you clear the mobs running out of the throne room and move deeper into the room, more and more new ones will aggro on you. And so on until three unique mobs remain in the room: Alfred von Hellmann, Giselle von Hellmann and Lidia von Hellmann. Alfred and Giselle are weak, it is not hard to bring them down, whereas Lidia is the key mob with a large amount of HP. It is by her that it will be calculated which clan gets the clan hall. That is, each clan must try to deal the greatest damage precisely to Lidia; the rest simply does not matter.
After you bring Lidia down, all the other mobs disappear too, and the damage is counted among the clans registered for the siege. After the count the clan that captured the clan hall is announced. Damage dealt to Lidia by sympathisers not registered for the siege is not counted. If Lidia's HP is not taken off during the siege (and it lasts 1 hour), there will be no winner, and the clan hall will pass under the control of the NPCs. That is, you can invite helpers from other clans to the siege, but they should be used either for farming the ordinary mobs or if you see that you will not bring Lidia down without their help.
After the victory in the battle for the clan hall you can switch on all the services at the manager, the same as in ordinary clan halls: buffs, teleports, item creation. Since the clan hall is elite, even C armor scrolls are sold here. And what is most interesting, it is precisely here that I found the recipe for crafting the 
Feathered Hat on sale, although it would seem it should be sold in the Devastated Castle.