The Peter and Paul Fortress was the first structure Peter the Great built in Saint Petersburg, Russia in 1703. Today it marks the founding of the city, but the fortress was used as a political prison for centuries and the cathedral holds the tombs of the Romanov Tsars. The Peter and Paul Fortress sits on the northern banks of the Neva River, and the tall golden spire of Peter and Paul Cathedral marks the location. This spire was the tallest point in Saint Petersburg until a television tower was built in the mid-1960s.
Cruise ships sailing northern Europe and the Baltic Sea include shore excursions to the Peter and Paul Cathedral, as do river cruise tours sailing between Saint Petersburg and Moscow. I found the Baroque architecture of the cathedral fascinating, especially since it is so different than most Russian Orthodox churches.