The Peter and Paul Fortress is the original citadel of St Petersburg founded by Peter the Great in 1703 on the North bank of the river Neva.
We didn't go into the barracks or its notorious prison cells.
We did visit the Cathedral precincts. The Mint is still in use.
The main building of interest is the Peter & Paul Cathedral built by Peter the Great. It is the main Romanov family Cathedral with the tombs of most of the Tsars from Peter the Great onwards.
Peter the Great had this new Cathedral built in the European style, which caused consternation among the conservative Russian Orthodox establishment.
For instance, you can see straight through the Iconostasis to the altar and there was a pulpit!
Where would these new-fangled ideas lead to!
Alexander II was a reforming Tsar, getting rid of serfdom in the country in 1861. Days before he was about to create the Duma (an elected parliament) in 1881 which would have significantly altered the politics in Russia (and maybe avoided the 1917 revolution) he was assassinated. His grandson, the future Tsar Nicholas II witnessed the assassination, but unfortunately Nicholas II was a totally different character to his grandfather. The rest as they is history and you no doubt know well Nicholas II's fate. (A fascinating book I read recently and would recommend is Miranda Carter's "The Three Emperors - Three Cousins, Three Empires and the Road To World War I" The three cousins being Nicholas II, our George V and Wilhelm II)
80 years after their assassination, the remains of the last Tsar and his family were laid to rest in this side chapel of the Peter & Paul Cathedral.