The speaker rejects the usual comfort that a dark time will pass. Others say the tunnel is temporary and the light will return, but the speaker insists there is no way out, because the tunnel is everything that exists. The "life outside" (wind, sea, flowers, freedom) is dismissed as an illusion.
What makes the poem unsettling is that the people inside are content. They feel "lucky and loved and blessed." They mistake concrete for beach rocks, smell scents in odorless air, hear lovely music in echoes of steps nobody took, and see fireflies in what is only dust. Their happiness is built from small self-deceptions.
The tone is flat, bleak, and quietly ironic. The speaker seems weary and distant, neither angry nor hopeful. It's hard to tell whether the poem pities these people or envies them, and that uncertainty is what lingers. It may be about depression, or about how we invent beauty to survive a closed-in world.