Peter the Great began the massive Peter and Paul Fortress, the first building in his new city, in 1706. The citadel has a dark history as a prison - no one every escaped - and execution grounds. Revolutionary figures like Trotsky, Gorky and Lenin's older brother were jailed there. Now a museum, the fortress has a display of torture methods used, but it also offers a collection of architecturally interesting buildings including the Russian mint and a cathedral where Romanov tsar are entombed, beginning with Peter the Great himself. There's a fee for entering the fortress, but walking around its walls is free. Nearby are places to board a tour boat or sun on sandy beaches. Gorkovskaya is the metro stop.
Peter and Paul Fortress, Saint Petersburg, Russia