Link's Awakening.
I have such strong memories of 11yo me playing this game on summer vacation. My father had bought me the game in America before LA even came out in Europe, and for all I know I could be the only Italian kid playing this game in the summer after finishing elementary school.
I could barely understand English back then, yet the game was accessible enough that I didn't need to understand every nuance.
I remember getting stuck for what seemed like weeks in the dungeons in the second half of the game, while it was probably a day or two for the hardest puzzles. I remember my jaw literally dropping when, by pure chance, I found out what to do in the Eagle Tower. I remember every step in the trade chain and not even understanding what the Magnifying Glass actually was or what it did. Some of the stuff in the game just seemed to happen by itself, I was often just fumbling around in the overworld and underworld, finding new stuff and then having it work in ways I didn't even realize. I don't remember making the connection between the magnifying glass and the library book, for the longest time I thought the book contained some horrible secret before... something in the game happened and suddenly you could read the book's contents, LOL.
That was one of the last times I figured out everything in a game by myself. Other games I could find guides on magazines and books and in school I could share tips and secrets with my mates, but LA was completely new and I was the only person I knew with a copy of the game, so I had already finished it by the time it came out in Europe and some walkthroughs started appearing in magazines.