The following contains spoilers for people who have not read the original visual novel or any of its translations. I repeat! The following contains spoilers for people who have not read the original visual novel or any of its translations.
I am not responsible if you ruin the story for yourself.
Shirou’s (and, by extension, Archer’s) Unlimited Blade Works is a canonically barren wasteland with nothing but swords and/or cogwheels. This is shown in the second season’s opening animation: Shirou and Archer are alone within their wasteland of swords.
Interestingly enough, the ending animation has a fairly neat and original spin on Shirou’s mental world… Shirou is no longer alone in his field of swords; Rin is now with him. His Unlimited Blade Works is no longer a wasteland; rather, it’s full of life. Luscious green fields now cover the once-barren plains and Archer’s signature cogwheels are now inactive/broken. With Rin by his side, he will not end up like the Shirou that became a Counter Guardian.
Thumbs up, Ufotable!