Black Chasm Cavern in Volcano, California is a hidden gem filled with millions of delicate crystal formations called helictites. In fact, it's one of the largest concentrations of helictites in the world! These twisty wonders are like the fine China of the natural world—look but don't touch! The cavern also houses stalagmites and stalactites, colorless crustaceans, and rare arachnids in its dark lakes. Guided tours are available daily for those brave enough to venture into this chilly 58-degree underground wonderland.

Pet-friendly: No, pets are not permitted.

Soft adventure: Yes, absolutely! Although there are some steep steps entering and exiting the cavern.

Seasonality: Technically all seasons, but there may be road closuring during the winter.

Fee: $22 per person