Peterhof is famed largely for its fountains, which are both ingenious works of hydraulic engineering and masterpieces of monumental decorative art. The glittering, iridescent jets of the three cascades and the many fountains playing in the rays of the sun create the unique sensation of a celebration of nature and Peter the Great’s own favorite element — water. This is an open-air museum unlike any other in the world. Photos by Frederica Dunn