There is a mysterious container at the attic. There's no handle or anything to open it.
This is the low-spoiler guide for "Opening the container at the attic" puzzle in Gibbous - A Cthulhu Adventure. Unlike in normal walkthrough, you get gradual hints on how to solve the puzzle. Click the big button below to see your first hint. If the hint contains a spoiler, you will be warned about it before clicking.