VOLCANO — There’s an entirely different world underground in the 209.And one of the best places to explore it is the Black Chasm Cavern near Volcano.The cavern - a kissing cousin to the more advertised California Cavern featuring the state’s largest public cave chamber between Murphys and Columbia off Highway 49 - is a national natural landmark. It got that distinction because you will find rare - and stunning - displays of helictite crystals. They look from the ceiling.