Try to go with a private guided tour as the lines can be long and daunting. It will be interesting to hear the guide`s stories as there is a lot of history around this place. You can buy the tour at the Nevsky prospect opposite Zinger house (approx. 1300 RUB including transportation, guide and entrance ticket to the palace). Catherine Palace is opulent and the Amber Room is absolutely stunning. Gardens are beautiful. Great place to spend a day.