It's nicknamed the Venice of the North with 42 islands and 93 rivers and canals. Vodka. The further back in history the posher the vodka - Parliament, Putin, Tsarskaya or keep it simple with Russian Standard. During White Nights, normally lasting from June 11th to July 2nd, the sun never completely sets. 24-hour party anyone?
Don't go in January. Just don't. Unless you're a sadist. In summer, between 1am and 5am the bridges linking the various islands of the city are raised to let big ships pass leaving you stranded if you're on the wrong island to your bed. Perfect excuse for another drink and a sleepover. When the ice melts in April all the dog poo unfreezes. Cue serious smelly times. Learn a bit of the Cyrillic alphabet so you can read signs (bAP = bar to get you started).