Skyrim is a great game. It's huge, it offers up many, many hours of gameplay and quests, and people are still playing it extensively to this day. Some of those people are the PC modding community, and they're building 'Beyond Skyrim'
Beyond Skyrim is a collaborative effort in the Skyrim modding community over on Dark Creations' forums. They are creating the other provinces from The Elder Scroll's world of Tamriel, starting with The Elder Scrolls IV: Oblivion. There's currently no scheduled release date for the mod, but you can watch its progress on the forums, or even sign up to help out on the project.
The latest trailer of the mod, in celebration of its third year in development, shows the Cyrodiil, High Rock, Hammerfell, and Roscrea areas.
There are a wealth of mods available for Skyrim now, in the Steam Workshop and on Skyrim Nexus, so if you've played the game and finished everything, why not head on over to the sites and mod the game for something new.