Wikipedia
Iriy
Iriy, Irij or Vyriy is a mythical place in Slavic mythology where birds fly for the winter and souls go after death, sometimes identified with paradise. Snakes have their own iriy where they go for the winter which is located underground.
The term was first mentioned in the writings of Vladimir II Monomakh. During the Christianization of Kievan Rus', people were able to imagine heaven and hell based on the idea of iriy.