Iwami Tatamigaura is located on a hill whose point protrudes into the Sea of Japan, and is elevated approximately 50 meters above sea level. You can see a steep cliff tha was eroded by the waves of the sea, which is known as a sea cliff. It stands 25 meters tall. There is also a flat seashore that is spread across an area measuring about 49,000 m2. This flat seashore is called a wave-cut platform. You can see fissures running up and down the length of the seashore that resemble a tatami mat covering the surface, and thus it became called "Senjojiki" or "Tokonoura." The meaning of "Senjojiki" is 1,000 tatami mats, and "Tokonoura" refers to the seashore looking like a floor made from tatami.
If you go through the tunnel, you can explore stratums from over 1,600 years ago where there are numerous fossils of shells and whales, and round stones shaped like stools called "nodules" that were formed by erosion. There are also a vast number of faults and sea caves that you can see. Iwami Tatamigaura became designated as a national natural monument in 1932.