%LOCALAPPDATA%\Packages\MattMakesGamesInc.Celeste_79daxvg0dq3v6\SystemAppData\wgs\ ~/Library/Application Support/Celeste/Saves/ Linux
Once inside the root directory, the most important subfolder for modders and curious players is the folder. This directory houses the majority of the game's assets. Unlike modern engines like Unreal or Unity, which pack assets into large, unreadable binary blobs, Celeste uses a relatively open structure that allows for easy inspection.
Editing game files ranges from harmless fun to save-corrupting chaos. Always make a backup before changing anything.