The “mega pillow” of Su Carongiu de Fanari owes its name to the geological origins. The characteristic lava flows, formed by undersea eruptions, are similar to blocks and remind of pillows. These kind of lava rocks normally measures up 1-1,5 meters, while mega pillow consists of a block that measures about 12 metres length and 8 metres high, representing one of the largest lava rock in the world, in that shape. The undersea eruption which led to mega pillow formation, occurred about 20 million years ago. The radial fractures on its surface are due to the  sudden cooling of lava flows coming into contact with the seawater.  Because of its  peculiar features Mega pillow has been officially recognized as a Sardinian Natural Monument. The current structure of the surrounding territory depends on the erosion activity of the last 2-3 million years. This Natural Monument is located along the SP44 road km 9,2, (free access and free parking area).