Steam soundtracks are installed and displayed as a separate library item from the main game (also, they can be purchased without owning the game).
When installed, there is a "Browse Local Files" button beneath the "Play Album" button which will open up the folder.
Some games, such as Shadowrun Returns, which predate Steam's soundtrack system, settle for installing DLC "goodie packs" containing music, pdfs, and whatever else as a folder tucked away in the game directory. An in-game button that opens up that folder on behalf of the user would be ideal, but that's not always provided.
When installed, there is a "Browse Local Files" button beneath the "Play Album" button which will open up the folder.
Some games, such as Shadowrun Returns, which predate Steam's soundtrack system, settle for installing DLC "goodie packs" containing music, pdfs, and whatever else as a folder tucked away in the game directory. An in-game button that opens up that folder on behalf of the user would be ideal, but that's not always provided.