One of the string of limestone caves threaded along Caves Road south of Margaret River, Mammoth is explored self-guided with an audio player, at leisure and largely alone. Boardwalks descend through vast, raw chambers of fallen rock and flowstone, and the cave is famous for its fossils - the jawbone of a Zygomaturus, an extinct giant marsupial, is preserved in the wall where it was found. Cool air pours from the entrance even in high summer. Between the karri forest above and the surf coast a few minutes west, it is the most atmospheric of the region's caves for those who like to set their own pace.