Make Your Own Virtual Reality App for Google Cardboard on iOS

(These notes are relevant for Unity version 5.5 and under. Here is a new post that covers Unity 5.6, when the Google Cardboard SDK was integrated into Unity build settings, making some of this obsolete.) I thought Google Cardboard was neat when I first saw it but a couple days ago I started playing around with creating 3D content for it and I'm blown away with the possibilities. I want to give a survey of some ways 3D content can be experienced in a Cardboard VR app but I'm not going to go super in-depth with any of them because each one is its own endless rabbit hole. The biggest hurdle, especially for making an app for iOS (as opposed to Android) is getting your Unity and XCode environment set up. Once that's working the rest is pure fun and amazement.