Thulsa’s Xoth campaign The Spider God’s Bride should fit right in.  Also, individual scenarios from his Ancient Kingdoms: Mesopotamia would also have the right vibe IMO.  

Yeah; Cyclopean Deeps has come up before, but I'll add that it's the most interesting take on the Underdark that I've seen (Operation Unfathomable is  decent, but a bit goofy) and seamlessly fits the Hyperborean setting.  Hell, he's got Leng Spiders in there, which obviously I agree with.

And I didn't go back through the whole thread so I may have missed it, but Anomalous Sub-surface Environment would certainly work too.