It involves sneaking one person around to Pondmuk and learning the password. That way, the party can go through the door by the entrance and just fight the guards instead of everyone on the level.
Alternatively, you can send a few fighters invis all the way around to the back side of the door, and have them kill the guards. It's faster than doing Pondmuk, though I recall you get some XP from him. Either way, if you haven't fought any of the clans, then you get some experience when you go to the next level (of course, after that, you can wipe out everyone if you want to
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Nightowl2