Earlier in my travels, I came across a dwarven ruin. Traversing through it, I found one of those pedestals you put that key in to open it. A couple I already know lead to Blackreach, however this one I think was different. I just can't remember where it was.

Also, on a similar note, those big round structures that house both the item you need for the Mages Guild, and the other one for the main questline, are they the only ones out there holding valuable treasure, or are there other places too? I think I've travelled all I can of Blackreach.

Anyone?