"Piter" is traditional Russian slang for St. Petersburg. It was also applied to Leningrad 1918-1991.
The St. Petersburg Metro also doubles as a bomb shelter, necessitating the need for special permits when filming inside these locations. Passengers are forbidden to photograph the inside of these stations although they are among the most beautiful.
The film's tagline "Second film of the year" references the tagline of Day Watch (2006): "First film of the year".