We took a one day tour to Novgorod, visited all the top attractions in Novgorod. Although it is nice, it is far less impressive than St Petersburg and the Moscow Kremlin. We stayed 7 nights in St Petersburg, barely had enough time to do/see everything we wanted... So, my recommendation is to skip it if you have less than a week in St Petersburg. The longer you stay in St Petersburg, the more things you will find to do. The city itself is like an ever ending fairy tale with so much to offer.