A tunnel differs from a maze or forest in one important way: it implies a single, defined path through a difficulty, with a clear entrance and exit — even if you can't see the far end yet.
Walking through a dark tunnel toward light
This classic version often reflects genuine confidence that a current difficulty has an end point — even if you're in the hardest part of it right now, some part of you trusts there's a way through.
A tunnel with no visible end
Can reflect a difficult period where you haven't yet been able to see or believe in a resolution — worth distinguishing between genuine uncertainty and a temporary loss of perspective.
A tunnel that collapses or is blocked
A more anxious version, this often reflects a fear that the path you'd counted on through a difficulty is no longer viable — you may need to find a different way through.