My time to shine. . .
Yes, St. Petersburg is where all the cool people go, but it's not just for the Hermitage. The city is full of old museums and historic spots. You can view Dostoevsky's apartment, now a museum of the writer's life, and also the flat where the murder in Crime and Punishment happened is still there, or at least it was in 2006.
A day trip to Kronstadt is also an option, as are Tsarist era palaces in the suburbs. But don't expect anything that commemorates the mutiny when you go to Kronstadt, that's all.
Just make sure you get the visa. People can be and have been turned away at the border, because they think the chit you need to prove you have accomodation in Russia is the actual visa itself. It isn't, it's just one of the key things you need to clear the bureaucratic hurdle.