Near Plymouth is The Black Chasm Cavern The Black Chasm Cavern was designated a National Natural Landmark in 1976 by the National Park Service in recognition of its outstanding natural beauty and geological significance. Visitors to the cave are enchanted by the beauty of a wide variety of formations including stalactites, stalagmites, flowstones and the vast arrays of rare helictite crystals.

The 50-minute Landmark Walk Tour follows a series of platforms, stairs and walkways designed to give the best views of the cave without compromising the naturally pristine environment. Currently, the tour culminates in a visit to the Landmark Room, the location of the greatest collections of sparkling helictite crystals.

There is a Visistors Center providing information about the cavern, outside the there is gemstone mining at the mining flumes.

The Cavern is open every day of the year, tours leave approximately every 45 minutes throughout the day. The Cavern is located at 15701 Pioneer-Volcano Road near Volcano.