National Landmarks are cool places to visit, but Colorado has one that is too deadly to visit.

Sulphur Cave, just west of downtown Steamboat Springs is one of the country's newest National Natural Landmarks, having received the designation in January. That is pretty special, but don't plan on a visit any time soon. Sulphur Cave features a highly toxic environment filled with dangerous amounts of hydrogen sulfide and carbon dioxide gases - deadly to humans.

According to CPR.ORG, Sulphur Cave gets its name from the way it smells - that familiar rotten egg smell. There is a lack of oxygen inside the cave, and the specialists who have been privileged to explore the cave have had to have fresh air pumped in.

Inside the cave, explorers have found "snot" drips  called snottites hanging from the ceiling which have been described as "disgusting looking."  The National Park Service says these are mucus-like soda straws containing bacteria. They metabolize the hydrogen sulfide gas, and then excrete sulfuric acid in the process.

Explorers have also found blood-red, brownish worms called Limnodrilus sulphurensis. These red worms are about an inch long and live in the water in twisted masses. These special worms are only found in a few places on earth.

The National Natural Landmark designation is given to select sites with significant natural features. Sulphur Cave is one of three new NNL sites designated in January, along with Bear Rocks and Allegheny Front Preserve, West Virginia and Lanphere and Ma-le'l Dunes, California.

As you can tell, Sulpher Cave is a super cool Colorado place, but the vast majority of us will never get to see it and experience it in person. Still, just having something like this in our state is pretty awesome.

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