This image shows about 1/3 of Red Square - it is simply enormous.  The center of the square (actually a rectangle) is surfaced with cobblestone.  On the left is GUM and right center is St. Basil Cathedral.

Additional comments provided by Julia Ekimova

The name Red was given to the Red square as red was considered a particularly beautiful color (it has something to do with Slavonic tradition of homage to the Sun and it’s symbols) The translation "Red Square" (instead of "Beautiful Square") which is now universally used, became established only in the 20th century
Red Square, with an average length of 400 m (440 yd) and average breadth of 150 m (165 yd), is the central square not only of Moscow, but of the whole of Russia. Since the time of Ivan III(15th century), this has been the scene of great public events, mainly political - rallies, demonstrations, and processions. In earlier times, Red Square was also a place of execution.
Originally the approach to the Kremlin from Red Square was protected by a moat, 32 m (105 ft) wide and 12 m (40 ft) deep, between the Neglinnaya and the Moskva Rivers. During the reconstruction and rebuilding carried out under the direction of Osip I. Bove to repair the damage caused by the French in 1812, the moat was filled in, the Neglinnaya was bricked over, and the drawbridges in front of the Saviour Tower and St. Nicholas Tower were removed. Russian people say: "Red Square is the heart of Russia".