Like you sort of included, a big part of the landscape is the architecture and society that inhabits it.
For me the winner is the Telvanni towers. Those giant mushroom towers were alien, mystical, architecturally interesting.
Forgot about those, nothing can quite match the wonder I felt when I arrived at a Telvanni-controlled settlement for the first time, I think it was...oh jeez it's been so long, what's the name of the settlement that has that insane Telvanni mouth or something there, and a group of rebels outside the city trying to overthrow her? Man, I'm gonna go play some Morrowind