Unfortunately, I can’t write what’s behind the door, it would be a huge spoiler :)
What specific key you can't find? Initially, I wanted to make it so that the branches with keys would be indicated by notes, which could be seen directly from the main path (the one with the arrows), but it was too simple, so I hid them a little. In general, if you found a note, then you are on the right track (Posters about missing dogs do not count!). If you are completely lost in the maze, you can go along the left wall - it always works.
Thanks for playing, I appreciate it!