Where It All Goes Down
Gramarye (England), the Middle Ages
We're not meant to think that this book takes place in the real England. For one, England wasn't ever known as Gramarye. Secondly, there's no such thing as Questing Beasts, or demons fathering time-traveling magicians. At least that we know of.
Instead, White creates a fantasy version of medieval England with lots of historical flavor dropped in. There are technical details on hunting, jousting, architecture, art, manuscripts, botany, woodcraft, and clothing, all of which lend a quasi-realistic feel to the novel(s).
White also keeps it real by making sure we understand that it's not all fun and games in Arthur's England. This is a dark place in a chaotic time, where bloody barons do unspeakable things to their vassals and where the strong rule the weak. This isn't a completely romanticized version of the Middle Ages. It's a blood-soaked hellscape that makes Westeros look like a nice vacation destination.