Out of all the places in Skyrim, marked and non marked, Vanilla and DLC locations included. Which would it be and why?

For me personally, I would like either the Volkihar Castle ruins. With all the rubble removed, broken furniture replaced etc. Mainly because of how secretive and forgotten it is.

Another place I'd like would also be Septimus' Hideout. Simply because its so far out and hidden.

What about you guys?