If you purchased the premium version, here’s how you can download music and wallpaper.
Wallpapers and music
Select” View” tab located in the top left-hand corner of Steam, and then click “Music Player.”
Music and Wallpapers:
Find the Planet Zoo installation folder, typically located within:
C:\Program Files (x86)\Steam\steamapps\common\Planet Zoo\Soundtracks (or Wallpapers).
Other interesting Planet Zoo guides – barriers, staff and guest guide