Portals into other worlds

One key technique used in fantasy is the notion of a 'portal'or 'doorway' into another world. There are many examples of these portal fantasies and listed below are some of the most well known....

The rabbit hole in Alice in Wonderland by Lewis Carroll
The knife in His Mark Materials trilogy by Phillip Pullman
The brick wall in Stardust  by Neil Gaimon
Platform 9 3/4 in Harry Potter by J.K. Rowling
The wardrobe in The Chronicles of Narnia by C.S. Lewis
The tornado in The Wizard of Oz by L. Frank Baum
The tiny door in Coraline by Neil Gaimon
The book in The Neverending Story by Michael Ende
A wizard in The Fionavar Tapestry Guy Gavriel Kay
Inkheart by Cornelia Funk
Elidor by Alan Garner
The ocean in The Darkfall Trilogy by Isobel Carmody
A virtual reality program in the Shalott series by Felicity Pulman
A gate in the Gateway series by Isobel Carmody

Movies
The stargate in the Stargate series 
The doorways in Monsters Inc 
The boardgame in Jumanji
The tree in Pan's Labyrinth by Guillermo del Toro
The map in The Time Bandits by Terry Gilliam