Astral Travel

There are many ways of travelling between the worlds, all difficult. One method is by astral travel, projecting oneself into another world while one's body remains at home; the disadvantage of this method is that one appears only insubstantially in the other world (one can, with difficulty, become more solidly in the other world, but this has the dangerous effect of making one less solidly in one's own world, with the risk of becoming lost and not being able find one's way home). On the other hand, being insubstantial, one is safe from harm.

A variation of this technique only available to people with more than one life (such as nine-lifed enchanters) involves travelling with one (or more) life while leaving one (or more) life behind - this allows the traveller to be solid in both worlds at once. However, any life lost while travelling in this fashion will also be lost when the traveller returns home.

Tacroy was the best astral world-traveller of his country and time, not counting those with more than one life. (This may have had something to do with the unusual disposition of his soul: see The Lives of Christopher Chant (spoilers).)