This is such a cool idea! Okay I am a big sci-fi and fantasy nerd so I am going to take this in a whole nother direction.

As Zoe peers into the darkness the floor again slumps and caves in depositing her alongside Marcus below with no way back up. They explore the cave below searching for a way out when they stumble upon a huge cavern dimly lit with a red light cast by the 3 eyes of an immense and misshapen stone idol in its center. They explore a labyrinthine network of worked passages surrounding the idol cavern, discovering strange artifacts of unknown origin, purpose and composition. The walls are covered in undecipherable petroglyphs. Eventually they emerge on the floor of a huge canyon by the banks of a river. The sky and air is alien, the rocks red. They are on Mars, albeit a Mars with an oxygen rich atmospheric layer which hugs the canyons and rifts. End Chapter Two.