We did a Royal Caribbean cruise tour in 2007 that spent two days in St Petersburg; we did the cruise's day tour which included the Hermitage, which was for me the most interesting part of the day. Saw masters' art work that you couldn't find in the books, probably because the western authors couldn't easily get there in the day.
We had lunch at the Radisson, where we were served by a platoon of precision servers, and they gave my 16-year-old son champagne and vodka... he was impressed! Mom was not...
Of all the travel we've done, that trip was my favorite: 4 days between Paris and London, then Oslo, Copenhagen, Stockholm, Helsinki, St Petersburg, and Tallin on the the ship. Found many places to which I'd eventually want to return for more. St Petersburg isn't one of them, however...