This app was mentioned in 1 comment, with an average of 1.00 upvote
mptp is right, locomotion with cardboard can easily induce sim sickness... Here's one app with a locomotion method which I thought was great: https://play.google.com/store/apps/details?id=com.pgcn.skeletonsthroughwallsvr The app itself is simple and could use more work but the way you walk resonated with me better than most other's I've tried. If the gaze is a bit below the horizon walking is initiated.