Something that totally shocked you learning it or realizing it. I might be using the wrong wording here, but ill give you my example:
In Ocarina of Time, we all know the Triforce was cut, or otherwise not something you get in the game, save for in the cutscenes towards the end. BUT - did you know you can actually go find it and see it in the game?
If you have a Gameshark, turn on the levitation code. Go go Zeldas Cortyard in the room where she is, and fly over the wall. When you fall, you’ll land in a pool of invisible water, and underneath the center of the room with the flowers, look down - there it is. Can’t interact with it, but you can see it, and i choose to believe putting it in that exact spot was intentional for lore reasons.
What do you got?
Maybe not favourite but the most recent i encountered and in surprising place: Path of Exile 2 which belongs to a genre not famous for even having much lore in the first place:
When you fight Doryani in act 3 he call you “Demon of Atzoatl”, despite protagonist of PoE 2 is not the same person as the protagonist of PoE 1 who travelled in time and ruthlessly pillaged the Temple of Atzoatl and by doing so possibly significantly influenced the fall of Vaal civilization and destruction of entire continent. But Doryani never met the MC of PoE1 and he possibly makes mistake because you too travel in time and do absolute mayhem at key time and place of the Vaal. What’s best: Doryani, while genius and one of the most impactful people in game world history, is a complete psycho and one of the worst mass murderers in history of Wraeclast but he figuratively* shit his pants on the mere thought of “Demon of Atzoatl” so it’s a nice detail too that finally some boss is scared of you.
*Figuratively because he don’t wear pants
PoE lore is absolutely great!
There’s also further funny bits. PoE1 mentions Doryani many times but never mentions what happened to him. It’s because he gets recruited by Alva to help MC in PoE2 (and gets demoted from chief thaumaturge of Vaal to free item identify bot). Fun fact is that Alva probably try to bluff him about the time travel and history, but she accidently hits the same theory as Ketzuli, Architect of Time and advisor to Doryani so Doryani believes that quite easily, especially that the Vaal cataclysm happens minutes later so it’s fait accompli anyways. And even better is that this theory is observably false since the atlas in PoE2 suppose to be Wraeclast after the cataclysm, but it has no sense at all with random placement and mix of everything. Doryani even notice that (though its too late) and comment that the reality itself is disrupted by the sheer power of the cataclysm, and warns MC that anything can happen, even meeting with another Doryani (which ofc happens, no way GGG is gonna waste a good boss on just campaign). Thing is, this makes the theories about determinism of history nonsense. And ultimately we know that of the Vaal traditions the only thing that gets preserved is their knowledge about thaumaturgy which only leads to even more tragedies as the recieving Azmeri later found the Eternal Empire which while less bloody than Vaal still abuse the thaumaturgy and fucks up the world again.