This story first aired on June 14, 2016.
It's no wonder Native Americans thought Sulphur Cave was a passage to the underworld.
The entrance sits within the city boundaries of Steamboat Springs, just below the town's iconic ski jump. Fences and signs keep people away from the toxic gases that waft out of the cave. Inside, blobs called snotties drip acid that can burn through shirts.
All that hasn't stopped Dave Steinmann, a cave biologist at the Denver Museum of Nature & Science. About once a year, he'll put on thick clothes and an oxygen mask, then drop in.
Why leave the oh-so-habitable surface? It turns out the gateway to hell could also be a window into alien worlds. "If there ever was a cave on Mars or in a moon on Jupiter...this is the type of ecosystem that could potentially exist," he said.
For evidence, he points to the blood-red worms he discovered in 2007. The worms don't need sunlight or much oxygen to survive. They make do with bacteria in the cave that lives off of hydrogen sulfide. Steinmann spoke to Colorado Matter's Ryan Warner just after scientists classified the worms as a new species this year.