Spotify's offline songs are encrypted and stored within the Spotify app itself, and they can only be played within the Spotify app. Spotify uses a digital rights management (DRM) system to protect the songs and ensure that they cannot be accessed or played outside of the Spotify app. Within the Spotify app, you can access and play the songs you've downloaded for offline listening without an internet connection. Please note that this feature is only available to Spotify Premium subscribers. But you could also use some third-party music converters such as DumpMedia Spotify Music Converter, TunesFun Spotify Music Converter, or TunesSolo Spotify Music Converter to do this.