World Walk

“When once the Kingdom of Mann is restored, perhaps then you might master the lost power of the World Walk—but for now, just plain walking is in order.”  "—the Raven to Einsa" The World Walk was an  ancient practice of crossing the boundaries between the Nine Worlds of Creation.

Necessary tools
World Walking could not be performed without specialized tools to open the barriers between Worlds. Dietrich had a ring for this purpose and the Great Hund had his Türs. It was said that other such devices once existed, but had been lost to time.

At the time of the events of The Sword and Its Servant, no being was capable of World Walking in the fullest sense of the term.