The Arvale Deluxe Contents are for the RPG Arvale.

They contain:
* 91-page strategy guide for the RPG Arvale (has maps, hints and strategies)
Includes several nifty bonuses such as artworks (old and new), comics, maps now and then, WIP drafts etc.
* Wallpapers 1920x1080
* OST
* Bonus Super Savefile

How to find the deluxe contents

From your computer, go to:
C:\Program Files (x86)\Steam\steamapps\common
Then select the game folder.

Or directly from the Steam Client, first right-click on the game, then select:
Properties > Local Files > Browse Local Files

EXAMPLE