So Cyrodiil's terrain was for the most part rolling meadows and such; pretty easy to get from A to B. Vvardenfell was smaller than Cyrodiil but felt bigger because it's difficult terrain made it difficult to traverse the province
Most maps of Tamriel just suggest mountains scattered about, but of course the specifics aren't set in stone. I personally think there should be a massive mountain range cutting through Skyrim (either east-west or north-south). Oblivion had mountains but they were pretty small, and if you ever reached the top, you would have to just turn around because you couldn't go down the other side. In Skyrim this mountain range would provide a really cool obstacle that you would have to travel through in order to get to the other half of the province. And there should be multiple mountain passages with dangerous creatures that would make it difficult to get through for low level characters.
That's just my idea, what are your's?