As promised ingame, here are some screenies I made of the instance we went in. Didnt turn out as cool as I hoped, but it roughly scetches the picture.
For those of you who werent there: We had to try 3 times to reach the end of the middle section, and trying some different tactics fighting nearly invisible skeleton archers we finally made it. And we found... TWO instances. One leading to Ard ta Feed
http://www.youtube.com/watch?v=JWETKZCtaNE(but this road was still blocked for us, for whatever reason), the other instance leading to Wight Lord Sothex, and quite an interesting fight!
First the room was pretty empty, so we started hitting this thing, which gave nice effects.

After some banging on the thingy, Sohthex appeared, who can do some nice tricks. Now and then he disappeared, conjuring some cool monsters, like the 3 undead constructs you see above (which made some of us inside go 'WHOOAAA!' on TS and the ppl outside go 'what? what? what?'

). On the next picture you see we slew the constructs and are fighting Sohthex again.

After some more skullbashing he disappeared again and we found ourselves being swamped by these skeletons. Too late we realized we had to destroy the pillars you see below.

So the party was all dead. Try again!?
Nope, unfortunately not... Somehow we respawned at the start of the other instance (the ard ta feed one, meaning 6 ppl had to get past undead constructs and invisible dudes again, which just didnt work.
End of the story: everyone dead (except Debaser

), but a real cool experience.