It is a special feeling: white night, music all over, people walking, young dancing....and the bridges raising. If you put San Isaac dome or Peter and Paul Fortress on the back of your picture, than you will have Petersburg essence. They raise the drawbridges in St Petersburg at night for larger boats to pass but this is for tourists and even locals not important: the event is to enjoy the atmosphere.
It is a tradition for even locals to go and admire the procedure, but be careful not to get stuck in the wrong side or you will have to wait until they close again.
Being on the Palace Bridge you can also see the next bridge to the opened.
You may thake the option of the raising drawbridge boat tour. You get a closer view of the spectacular occasion. Carefull at the price; make sure you discuss it before!!!!!!
I will suggest you not to miss the occasion.