You might want to spend some time browsing the exhibits at C-189 Submarine Museum, Russian Vodka Museum, or Erarta Museum and Galleries of Contemporary Art. Yusupov Palace, Mariinsky Palace, and St. Isaac's Cathedral are well-known local landmarks worth a visit. You can watch performances at Mariinsky Theatre, Arkady Raykin Variety Theater, and Tovstonogov Bolshoi Drama Theater if you're interested in local theater.