You need to enable JavaScript to view this site.There's a hole in the ground just west of downtown Steamboat Springs. What's inside is now a National Natural Landmark, . But don't plan to explore this place. It could be deadly. Sulphur Cave got its name from how it smells, "like that strong rotten egg smell," said John Spear, a professor of civil and environmental engineering at the Colorado School of Mines. He’s one of the few people to have explored this place. The intense aroma of sulfide means there's a lack of oxygen inside the cave. To explore it safely, Spear and his colleagues had...…You need to enable JavaScript to view this site.There's a hole in the ground just west of downtown Steamboat Springs. What's inside is now a National Natural Landmark, . But don't plan to explore this place. It could be deadly. Sulphur Cave got its name from how it smells, "like that strong rotten egg smell," said John Spear, a professor of civil and environmental engineering at the Colorado School of Mines. He’s one of the few people to have explored this place. The intense aroma of sulfide means there's a lack of oxygen inside the cave. To explore it safely, Spear and his colleagues had...WW…