LAST EDITED ON Mar-10-04 AT 11:16 AM (Pacific)The trapdoor can only be opened from the inside. And that's fairly close to the T'rangaporter too.
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To reach it you can either take the long route (from mine tunnels with pulse pick) or start combat as soon as the T'rang guard tell you to stop and then combat run past them. If you don't run in circles you should get just far enough to pass them (don't linger around too long on the other side though).
Alternatively you can also instakill the guards, careful not to hurt them at all. The game ai won't credit you with the kills, but the t'rang won't go hostile either. Well, the group you're trying to kill will go hostile ofc, but you won't mess up your faction rating.