You might want to spend some time browsing the exhibits at Erarta Museum and Galleries of Contemporary Art, C-189 Submarine Museum, or Alexander Pushkin Museum and Memorial Apartment. St. Isaac's Cathedral, Admiralty Building, and Strelka are landmarks that you won't want to miss. You can watch performances at Mariinsky Theatre, Mariinsky Theater Concert Hall, and Mikhailovsky Theatre if you're interested in local theater.