Saint Petersburg, known as Petrograd in 1914-1924 and Leningrad in 1924-1991, is the second largest city of Russia, with 5.4 million inhabitants (2018), and the former capital of the Russian Empire. Founded in 1703, it is not ancient, but its historical cityscape is remarkably well-preserved. The center of Saint Petersburg occupies numerous islands of the Neva River delta, divided by waterways and connected by huge drawbridges. Since 1991 it and some historical suburbs, including Peterhof, have been listed by UNESCO as a World Heritage Site. It is home to one of the world's largest museums of art, the Hermitage. Many Russians know the city as Piter, a familiar diminutive of Saint Petersburg.
Saint Petersburg was built by Peter the Great in 1703 on the Neva river, amidst the land he had just conquered from Sweden, outside the area populated then by the Russian people. Pre-planned rather than spontaneous almost from the very beginning, the city, called by Peter "my window on Europe", was designed to look European rather than Russian, and many European architects were invited to work here.
Saint Petersburg is simply put one of the greatest sightseeing cities on earth. No visit can do it justice—you'll have to move here to really be able to see all the sights. Really, budgeting a month of full-time tourism would not be unrealistic. And that's after all dramatic events of the 20th century that took place here! Perhaps only Rome, Paris and London can compare in sheer volume of beautiful, grand things to see.