Carlsbad Caverns is a fairyland, an underworld wonder whose formations daze the senses. This significant geologic phenomenon began to take shape six million years ago. The processes and chemicals that created these caverns were an exclusive combination—chiefly an ancient limestone reef dissolved by sulphuric acid—and the result was unusual and spectacular compared to other caves. Huge rooms in random patterns, capricious dead-end passageways, pits and chimneys linking different levels—these are the signatures of Carlsbad Caverns. The country underneath the surface is part glossy darkness, part cavernous hallucination. The twisting, illuminated walkway seems less like a trail and more like a venture across the River Styx and into the underworld.