You don't have to wait long. Another, much bigger explosion shakes the entire chamber. The guards become very frightened and, after a moment's discussion, abandon their post and race into the city to help with the fighting. You struggle against the urge to bolt for the gate, but manage to hold your ground until you are sure that they're gone.
The ground trembles as you emerge from your hiding place, and all around you can hear the ominous sounds of rocks splitting and cracking. The explosions have damaged the chamber, and stress within the rocks are now spreading the cracks and yielding the stone. You dash over to the gate and struggle for a few moments with the latch. Dust and small pebbles fall on your head, but you can hear bigger stones crashing behind you, near the center of the chamber.
The stones are heavy to move, and you struggle to get them open enough to slip through, knowing that at any moment the lizards might appear and kill you, or the guards might discover you and also kill you.
With a final heave, the stone door gives way to the tunnel beyond, and you dash through it. Behind you, you can hear more and more stones crashing inside the chamber. Dust rushes through into the tunnel and you find yourself running blind and choking on the ashen air. The sound of cracking stone fills your ears and you think that the tunnel is caving in too.
You keep running as the tunnel shakes and air rushes past you, carrying the dust of the large chamber ahead of you, but the heavy stones do not fall on your head. The sound of the echoing avalanche behind you is terrifying, for it is just behind you, and feels already past you. After several desperate minutes of gasping for air and fumbling through the dark passageway, the dust begins to thin and you are able to breath a bit easier.
You spend another hour cautiously making your way back through the tunnels that you used to get to the underground city. Finally, you count your blessings as you spy the sunlight peering at you through the cave entrance. You find your pack, cough out more dust, and solemnly head back to the village. You don't know what happened, but know you'll most likely die if you try to go back and investigate more.
The End.