What you're seeing locked are the "checkpoints" if you're on the Preview Screen after tapping a ride from the main menu (with the globe). Checkpoints demarcate 5 minute sections within the *same* tour you currently have selected.
We lock these because we don't want users to unintentionally start in the middle of tours thinking it's a different location and miss the great scenery towards the start. Not only that, the workouts are designed to flow smoothly from one checkpoint to the next. Starting from the middle makes sense if you're continuing where you left off.
Additionally the locks also show how much progress you have made through BitGym's content. Over time, the unlocked checkpoints will be a scorecard of how much you have worked out.
If you start from the beginning (the first available checkpoint which will be unlocked), you will seamlessly continue into the subsequent checkpoint. From the next time you select this tour you will find checkpoints you have reached to be unlocked, so that you can resume the tour from where you left off. The content is fully available to you.
Free Users For free users, only 10 minutes of a tour is available, and only the first checkpoint is available. Even if you clear a checkpoint they will remain locked while on the free tier. Once you subscribe any checkpoints you have cleared will be unlocked.
Free users will also find several tours on the main menu (with the globe) locked. If there are no available tours, try changing the circuit. All tours will be available when you subscribe.