Keep Defences
Brother Mac,
Actually he stated it was the dragon that set the Glyphs just inside the front door, but the defenses of the castle that we have discovered are as follows: -
1) Self repairing walls/Doors etc
2) Only one entrance (Confirmed)
3) Make food/water inside so no need to forage
4) 12 Elder Air elementals bonded to the walls
5) All walls and floors/ceilings are magically sealed so as not to allow TP, scrying etc
Inside the castle are other defences that the attackers are trying to get through (they need to get to a specific location within the Keep to raise BBEG) So far we know that there are Succubus and other creatures that the Orcs need to fight through, (Probably not hard with a dragon on the payroll)
Note: We've been told that we have to stop the ceremony to raise the BBEG (they will be sacrificing a distant family member), since we have characters that died we need to travel for two weeks there and two weeks back, giving them a month to bypass all the defences, We are likely to arrive and have no opportunity to make gorilla warfare

This is why I'm tending towards the "Undermine the mountain and give them one chance to leave" scenario. This way there is a chance I might actually get the Keep I risked my soul for. They need the keep - I don't, so I really don't lose out if I bury everyone inside at the bottom of a 100 foot chasm and collapse a cliff on top of them.