Well, Kiev is a European capitol populated by almost 3 million people. Which means that it has plenty of raputable liquer stores. The beauty part is that russians (ukrainians) are so hung up on their drinking, you can buy alcohol pretty much any time, anywhere. The only thing, if you're looking to purchase some decent booze, I would avoid "Kiosks" 聳 the poorley regulated street vendors. Other than that, just go to any "Gastronom" (food market), most of them will have a fair selection of whiskeys. In my book the best place to buy anything alcohol related is the store called "Good Wine" (metro station Klovskaya or just enter "kiev, goodwine" in google maps). It's well situated in the center of the city, so, grab a bottle of wine or whiskey and go sight seeing. In Ukraine there are no laws against open containers, so, that's another perk of getting hammered here. Just make sure to leave your passport and cash at the hotel. Cheers!
