If it isn't dark by the time you get out of the Hermitage then there's plenty more to see in the immediate vicinity. St. Isaac's Square, and the impressive St. Isaac's Cathedral is just nearby, and Kazansky Cathedral and Church on the Spilt Blood are also to be found in the very heart of the city.
After such a culture fix, shop-a-holics and anthropolists will be keen to take a stroll up the Prospekt Nevsky - St. Petersburg's very own Champs-Élysées. This enormous boulevard runs all the way from the Hermitage to Alexander Nevsky Square in the far South East of the city and affords plenty of commercial and people-watching experiences in a stunning architectural setting.
Meanwhile across the river from the Hermitage is another absolutely essential St. Petersburg attraction - St. Peter and St. Paul's Fortress. This symbol of the city sits majestically upon Zayachy Island and was built to protect the city in the event of a Swedish invasion and later served as a jail. Today visitors can pay a trip to the Prison Museum and of course the St. Peter and St. Paul's Cathedral.
If you can cover all of the above you'll have certainly got an excellent flavour of the city, however that's not to say there aren't many more sites and attractions for the eager tourist. Dozens of ecclesiastical treats spring to mind such as Chesma Church, Smolny Cathedral and the Alexander Nevsky Monastery, whereas there's no shame either in ditching the museums and churches and simply enjoying a waterside walk alongside canals and over the famed three hundred or so bridges. Come the evening and you can take in a refined ballet at the renowned Mariinsky Theatre, or explore St. Petersburg's rather raucous nightlife!
Finally, those with a little more time on their hands might want to venture further afield and visit some of the attractions outside the city. The impressive Peterhof Palace is best seen in summer when its legendary fountains are in full spray.