To the left of the large door to the south, there is a curved stairway. Go up it and find a switch at the end of the hallway. That should lead you to the next part of the level. You have a ways to go before that large door opens.
: Okay, I know I'm being dumb - but I'm stuck right at the start of Eternal
: Mark V: I can't believe it's not total carnage. Have dealt with the first
: three ambushes, but can't now open either the door into the circular room
: to the East, or open the large door to the South. I've tried all sorts of
: combinations of switches, and looking for trigger polygons all over the
: place. What am I missing?