Enjoy a private tour of both the birthplace of St Petersburg—Peter & Paul Fortress—and St Isaac's Cathedral, the 4th-largest cathedral in the world. Explore the fortress, learn the story of its origins and and visit its Saints Peter and Paul Cathedral, where Russian tsars from Peter the Great to Nicholas II are buried. Then head to St Isaac's, recognizable by its massive gilded dome. Wander the now-museum, taking in its superb mosaics and collection of paintings. Later, climb to the observation walkway at the dome's base for spectacular city views.