The Fortress of Saint Peter and Saint Paul is the original citadel of Saint Petersburg, Rusia. It was designed by Domenico Trezzini and funded in 1703, marking the foundation of the city. The fortress includes many remarkable buildings, being the cathedral of Saint Peter and Saint Paul, where the tsars since Peter de Great to Nicolas II and his family are buried, the most famous.

See http://www.saint-petersburg.com/virtual-tour/peter-paul-fortress.asp for more information from the Saint Petersburg Bureau of Tourism