It is an extraordinary rock bridge, formed by the turbulent waters of Kostino gully. It is supported by two columns. The height of the bridge is about 10 metres, the length is 15 metres and the width is 7 metres. The thickness of the roadway is 1.5 m.The Rock Window belongs to the same geological period as the Stone Wedding and the Stone Mushrooms.
Some of the most beautiful agates in the Eastern Rhodopes can be found in this area .