Sunset Achievement in The Mooseman
Return to the gates of the Lower World
How to unlock Sunset
Story-related; cannot be missed.
This achievement unlocks upon completing the game. Most of the game is pretty straightforward and just involves you walking right, but there are some puzzles you'll have to solve along the way.
A full video guide of the game and all collectibles is provided below courtesy of user Baddriver. You can follow along with it to obtain all collectibles or use it if you get stuck.