The Hermitage is the most amazing place you will ever visit. Make a lot of time to be there, and go during the tourist off-season if you can (during my visit to the Hermitage, it was so packed that people literally could not avoid being too close to the art, so the alarms were blaring the whole time).
It will help a lot, also, if you can manage to have a guide to the city and know how to read and speak a little Russian. As with all countries I’ve visited, people aren’t thrilled if you come in only speaking English, but they’re extraordinarily pleased with even the smallest attempts to speak their language. Reading Russian is necessary because many of the signs are not translated or transliterated into English, including street signs, subway stops, and other things you really need to get around.
A day trip to Pushkin (formerly known as Tsarskoe Selo) or Peterhof is also totally worthwhile, if you get the chance. Sankt-Peterburg
