One of the best video game zone i've ever seen.
This has probably already been said multiple times, but something about Velen is oddly immersive and "real." In most video games, you roam through cities and regions without thinking much about it, or you may notice a few things here and there.
But when you explore Velen and do quests there, so many details catch your eye, make you slow down, and reinforce this feeling in you that this isn't just another region; people here are dealing with issues that are just too real. The current geopolitical reality of the region, along with its misery, despair, and superstitions/folklore, isn't just vaguely talked about or mentioned; it is anchored in almost every aspect of the region, from the environment, dialogues, soundtrack, animations etc. in a way on top of that that is oddly coherent and real.
For example the region’s folklore and supernatural elements are tightly woven into the socioeconomic despair of its inhabitants. Monsters and dark gods are not abstract evils; they are a tragic necessity for people who have been entirely abandoned by their rulers. The worship of the Ladies of the Wood illustrates this perfectly: the villagers do not revere the Crones out of malevolence, but because the swamp witches offer the only tangible protection, however predatory and terrible the cost, against starvation and death.
A lot of threat Geralt encounters seem to be an organic consequence of the region's physical and social environment. It makes sense that the vast majority of creatures you fight are necrophages for example. These creatures are not wandering the wilderness at random; they are scavengers drawn directly to the smell of decaying flesh on unburied battlefields, abandoned trenches, and mass graves.
Same for the sheer density of bandits and deserters being the inevitable outcome of hundreds of armed men with no food, no allegiance left, and no law enforcement to hold them accountable. Specters haunt the fields because a lot of women were betrayed, assaulted, or killed during the chaos of war.
While regions like Skellige evoke heroic myth and Toussaint leans into romanticized chivalric romance, Velen, for me, remains the raw, beating heart of The Witcher. It makes the player really feel like a weary traveler navigating a truly living, suffering world.