Mammoth cave is the only cave that uses MP3 audio headsets for a self-guided tour.
Italicized text is from here.
Mammoth is an impressive, gothic-like cave that could easily be described as the perfect home for a caveman. Your journey into the cave begins via an elevated boardwalk through towering Karri Forest. As you approach, the mouth of the cave opens wide inviting you in to discover its vast chambers.
Mother Nature thought long and hard about creating Mammoth Cave. In this cave you can see all of nature’s fantastic forces at work. It is truly remarkable. At 500 metres long and 30 metres deep, you will observe many spectacular formations including the Mammoth shawl and the “Karri Forest” flowstone which resembles the unique karri trees of the region.

At the end of your journey through the cave you will climb the stairs up a magnificent doline and exit on the other side of Caves Road (which you have traversed underground).
This time, surrounded by Marri forest, you will have the opportunity to return to your starting point either via a direct trail or a more scenic route that allows you extra time to appreciate the natural surroundings.
After mammoth cave we went to Gnarabup Beach. It was the only day during our entire trip that it didn’t rain. A lot of people also took advantage of the beautiful weather to go to the scenic viewpoint overlooking the beach.
Rochelle and I were freezing while this guy was going surfing. There were already a lot of surfers in the water.
We had lunch at the Udderly Divine Cafe which was just across Candy Cow.