Story Seed - Junction

Image Source: http://www.boredpanda.com/abandoned-places/

The artificial stone of the stairs had barely held together as your party descended into the darkened tunnel.  With a terrific, thunderous crash they collapsed as you began to walk deeper into the dank tunnel.  Left with no way to go back to the surface behind you, your only choice was to move forward, following the light of your glow globe.

Wary for predators, your group moves slowly down the tunnel, the stark wall of synthetic rock showed great age, and cracks and crumbling sections riddled the surface.  Below, two conduits of glass or synth ran in parallel under your feet with no apparent function still remaining.  Suddenly you step out of the tunnel, and into a vast open chamber that begins to light itself from recessed panels, revealing mosaics of tile and glass and metal that decorate this long abandoned structure.

Perhaps further exploration will reveal its purpose, and a way out ...