Modder ‘El Ha’ has released a pretty cool mod for Fallout 4. The Wilderness adds a worldplace that is at least as big as Nuka World, featuring lakes, forests, ruins and an abandoned city.
In addition, this mod features a horror-themed main quest and a dozen of new settlement options. Naturally, it also packs new weapons, items, armor and music.
As the modder noted, the settlements range from small to mid size. Most of them are set up in a way that they are near to each other in town. However, they are also very far away from Commonwealth.
The Wilderness is 1.1GB in size and you can download it from here.
Speaking of Fallout 4, you may also want to check out the following mods. Fallout London is a DLC-sized expansion and there is a Silent Hill mod for Fallout 4, called Whispering Hills. There is also a 1.1GB HD Texture Pack that adds 10 thousand trees, a 3.7GB Mod that adds 14 different weapons, and a 3GB Mod that overhauls all buildings of the Commonwealth. Lastly, there is a mod that adds different/unique ending cinematics to all factions.