Once you have completed all your required assignments in Wizard City, Merle Ambrose will ask you to investigate Krokotopia.
Once you have been given that quest, you can access the Spiral door by entering Bartleby the World Tree.
Just finishing the crafting quest for Eudora is not enough. You must complete all your required assignments in Unicorn Way, Triton Avenue, Cyclops Lane, Olde Town and Firecat Alley.
