spoiler obviously
When it came to searching for the pills, I thought about the place they eventually were, but I tried searching the spaces around it.
Later on, by trial and error the game led me to it.
But I wonder, what was the clue that I missed or dots I should've connected?
Well, I did not think this was a "try until you get it" thing, even though it took me far too long to get to the solution (careful, spoilers): - there is only one space that you cannot go, and one of the texts even hints at it, saying "you need to get there by another way", or something similar - if you use the Diving Suit, your movement is always the move of a Chess Knight (exception might be if you dive into a Water space, but I am not sure). So what you need to do is figure out how to get to the isle (the blocked space) via a Chess Knight move. It's not totally trial and error, you just have to figure out how diving works, first...