The first chapter of the Beyond Skyrim mod introduces a huge portion of Cyrodil to your Skyrim playthrough.
Skyrim is already a massive game, but several modders have taken upon themselves to find ways it could be even grander. Beyond Skyrim is once such project, an attempt to recreate as much of the world of Tamriel within Skyrim. A daunting task, but the team has already released its first chapter, granting access to Bruma and the surrounding county. You can download the current version of the mod here.
Bruma is a city introduced in Elder Scrolls IV: Oblivion, located not far from the Skyrim border. Once installed, the mod version is seamlessly integrated with the core game, meaning you can just walk directly to the border and try out the new content.
And oh boy, is there content. Bruma's full scope is apparently 1.5 times the size of Bethesda's Dragonborn DLC. The mod contains an original story set 200 years after the events of Oblivion, which means there are many new quests to enjoy. Not only does the city include 70 self-sufficient residents, the surrounding county is filled with new dungeons and points of interest. The project includes over 24,000 new lines of dialogue, including recordings by professional voice actors from Dragon Age: Inquisition and Dust: An Elysian Tail.
And that's not getting into loot. You'll also gain access to new Cyrodilic weapons and armor, and can gather items and ingredients unique to Cyrodil.
The only downside? Bruma is currently only available for Skyrim's original PC release. The good news is Beyond Skrim's next step is to rework the mod for Skyrim Special Edition and Xbox One.