The Blue Cave

The tunnel underground was completely silent.

After the howling of the storm above, the silence down here felt strange and heavy, as if they had walked into the ear of a sleeping giant. All they could hear was their own breathing inside their helmets and the sound of Saif's metal feet on the rock: tic... tic... tic... tic...

The walls of the tunnel were smooth and glossy black, like glass. And round, like an enormous pipe. Their helmet lamps made small yellow circles on the walls, revealing lines and ripples in the rock, as if a river of fire had flowed through here billions of years ago and left its footprints behind.

"Lava used to flow through here," said Reem, touching the wall with her glove. "Exactly like a river. Then the outside cooled first, the rest kept flowing on the inside, and it left the tube empty."

"It's as if we're walking inside one of the planet's veins," said Jad quietly.

Reem looked at him and smiled inside her helmet. "That's a lovely way to put it. Are you sure you hate Mars?"