Rosphoto is the largest Photography Exhibition Hall in St Petersburg. They regularly open new exhibits and it's a great opportunity to get acquianted with archive Russian photographs or with modern artists. They have multiple halls here - the second and the third floor, and the one which you enter from the inside yard. There's also a bookstore with lots of editions on art and photography.
Bol'shaya Morskaya Ulitsa, 35, Sankt-Peterburg, Russia, 190000