In
Terry Goodkind's series, the
Sword of Truth, the Sliph was a woman made from a liquid silvery thing resembling quicksilver. The Sliph was used to travel almost instantaneously from place to place in the Old and New Worlds, the trip required you to breath her in, instead of
oxygen, or else you would die. This gave you a
euphoric sensation for the duration of the trip, causing you to not want to breath back in oxygen once out of her.
Richard discovered the Sliph in
Blood of the Fold in the Wizard's Keep (a
castle built by the
war wizards of ancient times). Later in one of the books (can't remember, I get the books confused from time to time because I practically inhaled one after the other) the origins of the sliph are revealed, all I'll say is she came from the great war between the Old and New Worlds, like the
mriswith and
gars, I don't to give out any
plot spoilers or anything.