For those interested in Google Cardboard I have a recommendation to save a little cash on the lenses. They recommend the Durovis OpenDive Lens Kit which currently costs $9.99 + $4.51 shipping and isn’t eligible for free Amazon Prime shipping. I was able to get good lenses by pulling apart a Hasbro MY3D Viewer instead. It’s currently only $7.74 on Amazon and is eligible for Prime.
To get the lenses you just need a small phillips screwdriver. On the inner section, opposite the flap where the smartphone is placed, there are four small rubber nubs you can easily pull up. Under each one is a small screw. After those are done the inner section easily slides out and you can access two more screws on each of the lenses.
The device itself won’t work for viewing most VR applications due to the offset of the screen separator inside the case, though if you chopped that out and slide it back to the center of the inner cavity it should work fine.