The 300 m high Megyer Mountain was created during the Tertiary period of geological history, during the Middle Miocene (Baden) volcanism, and its mass is mainly made up of chert-silica rhyolite tuff.
The approx. Volcanic activity that began 15 million years ago took place below sea level, and later the volcanic structures rose above water level. The sedimentation in the marine environment is told by the impressions of mollusk turtles (e.g. shells) mixed in the material of the rhyolite tuff. During the intense explosive volcanic activity, the glowing debris tumbled down the sides of the volcanoes like an avalanche and accumulated due to its high temperature. This is how the homogeneous, unstratified rock that forms the material of Megyer Mountain was created. After volcanism ended, siliceous solutions flowed along the fault lines and penetrated the rhyolite tuff. As a result of the post-volcanic activity, the softer parts of the rock body became more resistant to the effect of silicic acid, while some parts (such as the horzak stones) hardened, making the rock material of Megyer-hegy sloppy, "wasp stone".
After solidification, the products of volcanic eruptions impregnated with siliceous solutions became very hard and resistant, and their crystalline inclusions and cavities made them excellent for the production of millstones. There was already a millstone quarry on Megyer Mountain in the 15th century, where millstones were extracted and processed for centuries using similar techniques, tools and manual labor. The so-called "Italian type" millstones were carved in a block from the siliceous rhyolite tuff. Before the decline in production at the end of the 19th century and the cessation of operations in 1907, the average production of the millstone mine varied between 300-450 millstones per year. In the 19th century, the focal point of millstone mining moved to the neighboring Király Hill, where "French-type" millstones were already produced (the millstones were already assembled from several elements). To remove the bottom water accumulated in the mine, the deepening of the drainage ditch was started in 1844 and continued for decades in the southwest corner of the medieval Old Mine.
The lake that was later named "eye of the sea" was formed in the excavation pit of the abandoned millstone mine. In addition to the pond, the former miners' lodgings carved into the rhyolite tufa can also be studied. In 1997, the lake and its surroundings were declared a nature conservation area.