The Peter and Paul Fortress sits on a small island in the Neva opposite the Winter Palace and was the original founding settlement of St Petersburg. Inside the star-shaped curtain walls stand the gilded-spired Saints Peter and Paul Cathedral — burial place of the Romanovs — the old mint, the Trubetskoy Bastion prison where Dostoevsky, Trotsky, Gorky and Lenin's older brother were all held, and a string of smaller museums covering city history, space exploration, and the cosmonaut Yuri Gagarin.
The complex is a full half-day visit. The cathedral, with its impossibly thin needle spire and rococo iconostasis, is the standout, but the views back across the river to the Winter Palace and the Hermitage are equally good reasons to come. Each day at noon, a cannon fires from the Naryshkin Bastion — a tradition since 1873 — startling everyone who has not heard about it. The fortress is reached by a footbridge from Trinity Square on the Petrogradsky side.