White Nights is a Russian celebration that runs from May through July to welcome the summer. The celebrations weren't extravagant for most of the 20th century because of wars and revolution. Now, Russia's economy grew stronger and the life of the celebration grew with it. Cultural festivals are held within the months; Dostoevsky, held on July 3, celebrates local authors, and other festivals have performances of classical music, opera, and ballet. Even the clubs stay open until 6 am on the weekends. The festivals draw attention of Russian tourists. Most travel from Moscow, but some arrive from as far away as Siberia.
Read about a first hand experience of the White Nights in Russia from the New York Times: http://www.nytimes.com/2011/06/05/travel/russias-white-nights-in-st-petersburg.html?pagewanted=all&_r=0