I recently travelled to St. Petersburg with my family and must say that it was the best trip of my life. Initially we had planned a trip for just three days, but then decided against it and extended our trip to a five night-six days vacation. I guess this was a wise move as we got to spend quality time at each and every tourist spot without having to rush through.
We spent a whole day at the Hermitage. It you are planning to visit the Hermitage, I would advise you to book online and arrive early to beat the crowd. Do not miss out on the stroll in the nearby Summer Garden; the weather is on your side over there. It is definitely a lovely way to finishing your visit.
As we visited the city in August, we got to enjoy a cruise on the river Neva and see the city as well. I highly recommend this cruise; however the boats tend to run only from May to October, so plan your trip accordingly.
The church of the Savior of the spilled Blood, St. Isaac's Cathedral, and Peter and Paul Fortress are some of the other classic sights that I definitely recommend to all tourists.