1. They tunnelled into solid rock.

2. The rebels tunnelled out of a maximum security jail.

3. The rescuers tunnelled their way in to the trapped miners.

4. The barrier of poisonous gas appeared to be less penetrable than the rock that had been tunnelled through.

5. The tunnel acts as a barrier to invading microbes, and as such, tunnelled catheters are designed for short- to medium-term access (weeks to months only), because infection is still a frequent problem.