Where is the Passport?
The Passport menu can be found in the Day Realm by tapping on the airplane just below the main Portal.
What does the Passport do?
Completing a region found in the Passport grants a one-time reward of Rubies. After collecting this reward, the region icon will "grey out". The Passport will then let you quickly travel to each of the regions by tapping on the green "Go" button under each icon.