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I could be waaaay off with this, but that looks like where you face the Charr boss in the Primary Vanguard Quest "Warband of Brothers", in the Dungeon Cathedral of Flames.
If I'm wrong, then it at least looks similar, I was too busy ensuring I didn't screw up to really notice/appreciate the scenery, but those stairs & pillar's look familiar.
http://wiki.guildwars.com/wiki/Cathedral_of_Flames
I'm pretty sure that the place your refering to only has a single stair in the middle, and a small stair to each side from the big one as well.
I haven't visited enough dungeons to know enough to help you, though, Karn. I agree with Katarine that it does look like the Cathedral of Flames - possibly somewhere else down there?
nope thats not the Dungeon Cathedral of Flames
it has a big stairs in the middle and then 2 seperate on each side.
It's also quite possible that the area does not exist. Anet often releases screenshots of areas that are later either scrapped or revised. Maybe it didn't even make it into the final game?