What are your favorite sfnal worlds?

Victoria sez, "Underland Press and author Jeff VanderMeer are building a book of the top 30 science fiction and fantasy worlds–from Ringworld to Dune, from Middle Earth to Lankhmar and beyond. This link goes to the web form that allows readers to nominate their three favorite worlds, and gives readers a chance to write about why they love the world. When it comes time to publish the book, a few of the responses will be excerpted in the book itself (with the authors' permission, of course).

They're thinking of the book as a compendium of sorts, but also as a travel guide. We've all spent years in these worlds–in imagination if not in fact. This book is a both a walk down memory lane, and a place to start new dreams."